Well, a float plane won't help when it comes to the crashing part. Landing in the lake isn't the problem, it's the crashing that's the problem.

You could sheet the fuse in foam, and the added drag wouldn't be a huge deal. Most models are drag farms anyway, and our planes are so over-powered that you just wouldn't notice it that much.

Messing with the wing is more of an issue though.

If you are reall concerned, go foamie. Look at how planes like the JKAerotec and TufFlight combat planes are built. They are all foam, and the radio gear can be made totally water proof. I don't think you could sink one of those if you tried. So, look over the building techniques, whip of a foam cutter (not hard to make at all), and start building your own large foamies. Not hard to do at all.