I wonder how many members here started making their own boards as they got sick of off the rack options, or being steered towards something their available shaper was more comfortable shaping. Weighing ~220Lbs and being anti pointy nose in the early 90's left me few options I liked, and the shaper I turned to later taught me much about the shaping laminating processes, and made many boards with an outline and volume and glass schedule I wanted, and only once did I succumb to the potato chip disposable mentality of the mid 90's, and thoroughly despised that board..
Well before I actually started building my latest and likely last hollow wood wood, or any board, several years ago, I came here and learned of Probox's adjustability, as I had intended using fcs original plugs as I never had issues with those when they were installed properly. Knowing the huge amounts of time and effort I was going to expend on this board, I wanted lots of fin adjustability for fine tuning, and I love tinkering and experimenting.
I really like the long fin base of Probox. Much stronger and easier to make than two tab fcs, and would accept all those FCS fins I made/bought in the previous ~20 years, even though the flex at the tabs is not desirable to me. I dont like future's canted tabs, and I prefer the post glass installation of Probox, and the fcs1 plugs for that matter. I dont much care what is production friendliest. I essentially bought the installation kit for use on just one board, and likely could just have freehanded the holes and saved $$..
I've had zero issues with water seepage around the Proboxes, They are recessed into multilayered cedar of many different grain directions with some cloth between those layers, each box has its own stringer, glassed and sealed / reinforced inside the board and capped all 5 of my boxes with one piece of 1.43oz cloth. The cedar receptacles inside the board are basically the size of the router jig/resin dam, and heavily reinforced to other stringers and nearby boxes, and rails. So the box install is basically bullett proof in my board, but the grub screw weakness is a worry, Especially with the high aspect ratio fins I have been keen on riding lately.
I had tried to rebuild the broken probox but had some issues with being frugal by using old epoxy dregs in some nearly empty bottles not curing properly, and busted out the router and took many shallow slow passes after super 77'ing the probox jig back to the board in the right spot. The replacement process went smoothly, I capped the box with 1.43oz again and have surfed many dozens of sessions with the replacement box, whose cap I have not really properly sanded flat and made to look pretty, yet.
I was going to design and build something like the Kreg pocket screw jig for drilling new grub screw holes through the probox and inserts, and then precisely tapping these holes for grub screws, perhaps of smaller diameter than the standard. I have sucesfully cast threads around fine thread small metric SS screws in epoxy, but there is no wiggle room and cross threading the screws is too easy and stripping the fine threads using too much torque was also too easy. But the 10-24 grub screw threads are coarse and much further apart in comparison to m4.
The probox center fin box grub screws are weirdly angled, pressing into the middle of the fin tab at more of a 45 degree angle. It could have been designed so there would be more material between tab recess and grub screw for greater strength, but was not. Custom fins for center probox need the grub screw Receptacle flat be up higher on the fin tab.
I guess if Probox is defunct, these little details are of little consquence.
I though Lary Allison was still selling probox and probox fins for SUPs.
Probox Larry has not ben on sway's for ages but has a facebook page, if anyone does FB maybe they can get a response as to whether Probox is indeed out of production or get a line on some new old stock sitting in the rafters somewhere.
Here's the permanent solution to your problem. I've used both and these are literally better in every way, except that you have to commit to your cant.
I was always nervous about the amount of material left over the grub screws after sanding. I never had one fail but I was always paranoid that it would because the walls of the box are thinner and have less threaded area in support of the grub screw - due to the use of the inserts. As it turns out, I almost never took advantage of the cant adjustments except when I was swapping fin setups entirely to go from a quad to a twinzer.
So with Fusions or Gearbox I just have to commit to my fin setup from the outset and it's all good.
Sanding/routing Probox flat, if installed correctly with tabs resting on lam and not a thick hot coat, will not sand any of the box by the grub screws though. The inserts fit flush to the box before installation, and they 'should' sit flush with the box after sanding the insertless boxes flush with the hull.
There is just not enough material between grub screw and insert to begin with.
One can actually submerge proboxes slightly if they razor the tabs a bit so the box sits deeper in the board as resin cures. Then capping them less cloth need be sanded off to get it flush, then the inserts sit a bit recessed. Hard to get the cloth over the area between grub screw hole and insert though for adding strength to that area.
I think if one is sanding probox by the grub screws, and then the inserts sit proud, then the probox floated up during the install or was not pushed all the way to the lam with tabs resting upon it. I was using my extra proboxes upside down with 3 or 4 Lb lead fishing weights atop to prevent them floating up as Epoxy cured. Glad I read every Sway's thread on probox installs before I did my first one as this trick laid within. The 6 oz football patch under the box might swell and push the box up without weight atop it.
My Quad boxes which I either did not route deep enough or sanded the bottoms of the probox a smidge or both, got not only the lead weights, but a wood bar across both and then bricks for even more weight, as I could see more resin bulge out the sides with more downward pressure. Dry, I could not see if the box tabs were flush on the lam, but the resin bulging out the sides with more downward pressure indicated I needed to compress the 6 oz or 7.5 oz football patches I used in the routed hole under the Probox.
Does Gearbox allow for the fore/aft adjustment?
If I ever make another board with multifins, I Would go probably go for gearbox, over futures or fcs, assuming I could not get probox anymore and keep having issues with the grub screw getting ripped out.
You need to be careful with Probox. They have to be down in the guides properly or you will sand off too much of the top and the screw holes will fail. Routing out the box after failure is a pain because they tend to break up and pieces go flying. Always wear protective gear when you route out boxes.
Something I like to do with quads is set the cant on the fronts and back differently. I often set the rears with no cant, or I do 4 degrees in back and 6 degrees up front.
I have been adding glass over the boxes after installation too. A lot more work than doing a prelam box like fusion or futures, but the cant adjustments and being able to have large tabs on some fins make them worth the hassle.
I think Gearbox is a neat design due to the oval shape that's just the right length and width to support most fins, because it can be installed under glass just as easily as a Future box, because if you use the high density collars you're not only supporting the box better but you can also do a single-rout cavity, and because the top plate is trussed 1/8" below the top of the top-plate so you get a nice thick sandwiched top plate under the glassed cap. You can use FCS twin tab fins and have enough room to move them ~1/4" forward or back. Or if you're making your own fins you can build them with a full length tab that will never break.
And, it doesn't look like Gearbox sponsors any pro surfers or models so you're not paying for that BS. Robin Main is a legit shaper, fin maker and hellman, not a suit; so that's another plus in my book.
I should send flowers.
I have a bunch of ProBox boxes and inserts. Not sure of the inventory. I'd be glad to pass them along to someone who will use them. PM me.
all the best
Personally I'm always ready to learn, although I do not always like being taught. - Winston Churchill