I think one of the set screws was a little up when I sanded down my pro boxes. I accidently sanded a portion of the head of the screw. Then when I was test fitting my fins the slightly sanded screw started to slip/strip. I thought I could get it down if I was careful, but I ended up stripping it completely with the key (the hex part, not the threads). Now it’s half way in and I can’t get it out.
Maybe try an easyout,its like a small drill bit except the threads are reversed.If you have a low speed drill use that and be gentle,you should be able to run the easyout in the set screw where the alen key would go,it needs th be just a hair bigger than the hole though.It should grab and ease the screw on out without a problem.
try a Very Small Drop of superglue/zap a gap/5 min epoxy in the hole/stripped key combo. Let it set and see if you can back the setscrew out. Push down hard and turn gently.
Check the wrench…it could be buggered, not the screw…I’ve found that most of the supplied wrenches are pretty soft and often strip before the stainless screw will. The ones that come with a shiny chrome like coating are the worst.
Best to buy a few 3/32 hardened steel wrenches or a folding set with 3/32 included.
As for the present problem - if it’s not the wrench - try Keith’s glue method first…
I just use a cordless drill at low speed and a bit around the size of the wrench. What’s left of the socket hole in the screw will center the drill, just watch the angle. As you drill into the screw, the bit will catch about half way through and you’ll feel the screw turning in the box. Then reverse the drill and it should back out. If that doesn’t do it, you’ll already have a hole for the easy-out. 99% of all stripped finbox screws I do with just the drill bit. Make sure the bit is sharp and put some oil around the screw first.
I think the obvious solution is to route out the entire tail area to the deck glass, backfill with pour foam, laminate some doorskin over it all and then glass on a single fin.