I am used to fixing them with the "nut" exposed but this one is buried in.

Even as a temporary repair, could I just pour superglue or epoxy into the hole?

Any ideas welcome.

Hi

If the thread is damaged you may be able to drill and tap the next size up.
Failing this, drill the hole big enough to get the damaged nut out. Then glass or epoxy a new one in of the same thread. Hope this helps.

Easiest way is to drill a hole across the bolt hole and insert one of these .http://www.sunshinecoastsailboards.com.au/shop/spare-parts-repair/crossnut-detail

youll find the thread is tapped into the glass ,and that's what will have stripped. need to drill out the bolt hole so the bolt goes in easy , drill a hole across the bolt hole about 15-20 mm down , the hole needs to be the same as the outside of the insert , then just push it in , they have a slot on the end so you can spin it in the hole to line the thread up.

pulled me out of the **** many times , I had a bolt snap of in the thread once , inside the fin could not grab it ...tried everything I could to get it out , easy outs ect .... Ended up having to cut the broken bolt out with a grinder , made a big mess of the area around the fin where the thread is . Laminated the fin back up with epoxy and carbon , drilled out a new hole and inserted one of the inserts , still going 3 years later.

^ what he said, best to do both as if one has stripped the other wont be far off

Like this , the carbon one is the one I had to dig the busted thread out of , the other ones just stripped out.

Is there actually ones that just thread into the laminate? No barrel nut?

It's a Vector Canefire and there's no nut in it. the treating is in the fin head itself. I will have to do the very same repair on a Canefire 40cm. insert a bolt and mark the direction further down the head. Measure the vertical position of the nut on another tuttle head and drill a hole on the line you just made. Drill out the old threats so the bolt goes easily to the new nut position. insert barrel nuts and a bolt and glue the nuts in the right position. voila!

I had some fins with a stripped nut that I couldn't get the cross nut out for fear of breaking the fin so I just got some longer screws and the problem was solved.