I am about to start on a Teardrop after finishing a Epoxy composite boat. If the surface you are talking about is exterior I would say definately EPOXY!

Here is a source for epoxy by the quart or gallon. This epoxy is a resin and can be mixed with sawdust to make a putty, or with microballons to fill surface imperfections. I would also recommend the white epoxy primer and also the LPU 2 part paints. This company is also a fine source for marine plywood. Here is the site:
http://plywood.e-boat.net/products.php?id=6
If you would like to see the boat, it is at the Flickr.com site. Search for sandy claws.
Like boat building, teardrop building is more labor intesive than material intensive. It is false economy to use cheap materials!! The difference between the good stuff and the cheap stuff is very small looking at the big picture. Do yourself a favor, and do it right the first time! You won't be sorry!

Always do right. This will gratify some people, and astonish the rest! Mark Twain