Wouldn't that still require the underside to be flat?

One option I am considering is using a really wide (like 1/2" or bigger) drill bit, and from the underside use it to just level out a little circle, so the nut (or bottom of nutsert?) can sit flat inside said circle.

Was thinking that the furniture bolt would be inserted from outside the top. A threaded cam lock on the inside to cinch it up tight against whatever gasket material you use. The flat bolt head could be recessed and bondo'd so that it is not seen at all from the outside.

Another idea - set up on the inside a series of cabinet latches like those used on small tool boxes. You can even get the stretch rubber latches like you see on tilt front truck front ends. They also come available in a cam lock format. Drop on the top, snap the latches and away you go.

After considerin gseveral possiblities, the solution I came up to was a little different.
To remove the abgle, I created a small wedge out of PVC block, and epoxied it into the curve, then drilled through it. This created a flat bottom, so now a good ol' long bolt and wingnut will work nicely.

Here's a snap of it:



Now it's all structurally done, just needs final touches and paint.
There are a few places where it's hard to reach the bolt top and nut at the same time. I think I'm going to give a try to a nutsert/ rivet nut in the fiberglass to deal with this.
Supposedly they are OK to use on fiberglass - I'll be sure to use aluminum ones, so the pressure will be less when crimping it into place.
Does anybody have any experience with this? e.g. adding using rivet nuts in fiberglass?

They work on fiberglass boats, using a load plate in the glass.. Your application has a lot less stress.

Ah yes, so they do!
I guess my concern is not really w/ the stress and use once installed, rather what happens when you are crimping them into place.
I have never installed one, just seen them afterwards and seen many pictures of the installation method now. But basically they get drawn up towards the surface, splaying the sides outward and creating a ring on the backside, right?
I'm just thinking that in order for that crushing to take place, this must be a lot of pressure around the hole in teh fiberglass. I guess I'm just paranoid. I guess the key is to esnure the fastener used is the correct depth for the material, so teh aplaying is mostly below the surface and not inside of it.

Cool idea, I think you executed your plan very well. Looks great too.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

Next time around look into using what are called flanged rivet nuts and square base threaded studs. I have been so far unable to find the source for the furniture fittings I mentioned before. Take a look at what is used on a cheap upholstered kitchen chair and you will see what I mean. One type is a stud with a head that is the size of a nickel, but real thin - maybe a sixteenth. The other is a threaded 'tube' that has barbed edges on a nickel sized base - meant to lock into wood. Each of these could be molded right into the fiberglass so that you would have no through bolts, only a fastener on the inside, such as a round head bolt.

Would send pics but not sure how,

Nice work man <img src="/forums/images/graemlins/kewl.gif" alt="" />

When are we going to do mine? <img src="/forums/images/graemlins/cyclops.gif" alt="" />

Hey, i'm just up teh road. Pick a weekend and bring the beer!