Hey Taildragger...
Almost any ARF trainer will do. Your idea of GP floats is good too. I just would fiberglass them overall for durability and waterproofing. Some foam floats might be cheaper and eliminate the need for concern over waterproofing.
Personally I don't put my receiver and batteries in baggies. I figure the water is going to condense on the inside of the bag and get it wet anyway. I just mount my stuff up off the floor of the fuselage and check it every once and a while. It's also a good idea to spray the inside of the fuselage with some kind of paint to seal it so the water dosen't soak into the wood.
Have fun,
Peter