RE: pop bottles as floats?
I saw a large electric "old-timer" on 2 liter soda bottles at Havasu several years ago. The bottles were so draggy that he could barely taxi and ROG was out of the question. He hand launched it, flew it and then landed in the water.
BTW, he used a three float setup with a small bottle at the rear. With no step, there is no way the bottles would work in a two float setup.
Jim