2 newbie questions

Many door skins are not made with waterproof glue. They will fall apart, rather quickly.

I made an airboat out of a chunk of 2" blue building insulation foam. Easy, and about the right amount of investment, for the use it was intended for. It got much more use in the snow.

I've had great fun with solid foam hull airboats. Most of mine have been based on the smaller white styrofoam flutterboards, with a pylon mounted .15 to .25 in tractor configuration, and a single large air rudder on the rear of the pylon. The radio I put forward in a cockpit style radio compartment. They scoot along nicely, turn sharply and will run up the shore and over grass, though better with the .25 on grass. With plain foam hulls they get beat up in ground running, I found a couple of coats of polyurethane on the hull bottom helped durability a bit. Good cheap fun. Great cottage toy for the younger crowd (with your supervision of course!). I found that in a controlled situation, they are a great "here, you wanna try it?" type of vehicle, because people get the hang of driving them very quickly, especially kids. You need to hover over them though in case something gets out of their control. But they generally figure it out in about 15 seconds.. skilled video game fingers I guess.

I tried a foam hull with a Tee Dee .049 and the radios from a crashed Slo-V given me by a neighbor. I used 2" white styrofoam I picked up at a building site to make pontoons, epoxied on a piece of door skin and a pylon motor mount, and put on a coat of resin to fuel proof everything. My nephew and I had a great time while it lasted! With no throttle, beaching was the only way to stop it and the foam did not last very long, resin or not. That's why I want to go with wood for the next one.

I also threw together an electric version with the motor and prop from the Slo-V. Being an old furniture guy, I've tried some woodworking things playing with these two models. I used some light weight spackling as a dent filler and white shellac mixed 5:1 with baby powder as a sealer (it dries in 15 minutes and sands well). I painted the electric model with Krylon - again, fast drying. It did eat the foam where I had sanded thru the shellac, though! Finally, I found a foam glue at a craft store that works like contact cement, sticks like crazy, is 1/2 the price of the foam glues at my LHS, and weighs less than epoxy.

Finally, those with V-tail experience will get a laugh out of this. I put one Slo-V servo in each boat and swapped the receiver and battery back and forth. Would you believe that one boat turned better left than right and the other boat did the opposite? And so we learn!