Another tip: Wad up a paper towel and put it in the aiprplane at the balance point.
Whe you're done flying, toss it. Most of the water will have gone with it.

Most trainers have the round-neck tanks that stick through the firewall. Trainers float on the wing, feet up, nose down. If (when) the plane flips, water will come in through that opening or through the fuel line holes..

You can kill yourself trying to make a plane watertight. Wet happens. Slow-Stiks fly from water just fine with everything exposed.
Dry everything when you are finished, and put corrosionX on your receiver, speed control (electrics) and the connectors.