Hi all -
Regarding “proper” box installations vs box installations “not done right.”
There are several ways to analyze the issue. If you’re going to make meaningful comparisons, it’s not enough to say “proper” or “right”… too subjective.
It can be argued that a proper box installation might start with the number and spacing of the stringers when the blank is ordered. In my opinion, a good start to a solid box installation is a blank ordered with double stringers spaced just far enough apart to allow a box to be dropped in between them. This prevents the removal of nearly the entire stringer directly in front of the box when the hole is routed out on a single stringer board. I’ve seen countless boards cracked, leaking, or even snapped in two right at that spot (immediately in front of the box) where the stringer has literally been routed down to 1/4" or less to make way for the box.
On boards I do with double stringers, I score the foam on sides inside the routed box hole so there is a connection from the hole directly to the wood. This, in turn, provides direct resin/wood support to the sides of the box when the box is installed. I.E. the foam isn’t going to be compressed by side-to-side fin pressure against the box.
Bruce Jones (RIP) used to run advertisements in magazines showing two ‘mini-stringers’ - one installed on each side of the box. This is a good way but might not be as structurally sound as two stringers from nose to tail. It could argued that the ends of the mini-stringers might contribute to a ‘hinge point’ while a full length double stringer avoids that.
Actual box installation can vary from factory to factory and from board to board. I’ve always liked a fiberglass ‘liner’ inside the hole, followed by a fiberglass patch (or two) over the top. Some guys like a complete tail patch (very obvious with a tinted lamination) extending from edge to edge in the tail. They look neat but if the box hole is routed in after the hotcoat, you still won’t have any glass over the box/foam seam unless it is applied as a separate step.
I’ve done many single fin box repairs where it appeared as if the box was simply installed (over a single stringer that had been cut away in it’s entirety) with a batch of thickened/pigmented resin only… no glass liner and no glass over the seam. It saves time, saves money and provides for a board that will likely need repairs or replacement much sooner than anticipated by the new owner. It can even be argued that pigment added to the installation resin weakens the overall product.
Stuff like what I’m talking about might help explain the difference in price between a $500-$600 longboard and a $1000-$1200+ longboard. It might also help explain why a solid longboard built to last is going to weigh more than a disposable cheapie.
With finbox replacement, the installation process can follow any of the above methods and with equal results as a ‘new’ installation depending on the method. The single stringer board will still be missing almost all of the stringer at the front of the box. The choice of mini-stringers, a fiberglass liner, or a cap is usually left to the repair guy. If I were to ‘do it right’ and route 2 additional slots for mini-stringers, line the hole with glass and do a feathered-out ‘cap’ on a box replacement, I’d definitely be charging extra. It’s a lot of work!
In this photo of a Bruce Jones ad it might be noted that the ‘mini-stringers’ are actually inside of full length double stringers. 
PS - In the Harbour video, it might be pointed out that in severe side-to-side pressure situations, the edges of the fiberglass liner are still going to compress the foam on either side of the box. I’ve even seen the supposedly superior “Chinook” sailboard boxes easily stuff up the foam along the sides of a box… The resin adheres to the Chinook edges around the box just fine but nothing prevents the resin block itself from compressing the foam. That’s where double stringers come in to play.
