[scottyt]

if you want to fill with epoxy, you can fill it with micro ballons mixed, you can get it as light as you want, then cover it with glass and epoxy for strength. but the point of using foam for neutral buoyancy is a good idea. but you could also fix it with epoxy like i said and try to float it, if its close leave it alone, if its light drill some holes and epoxy in some lead. if its a little heavy there is not much you could do.