In a high-wing trainer, the protection you need to do for water damage is minimal....
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No, the more I think about it, Since this is apparently a short-term situation, don't do anything.

If you feel you MUST do SOMETHING, relocate your switch to inside the fuselage, activated with a wire pushrod (even a paper-clip). This way, splashes won't get inside the switch. You can do this in about 2 minutes. Most servo trays have provision for the switch mount already.

Just dry the plane out after you are finished. Remove the wing and check for water in the fuselage. It probably won't get any water in it if you don't dunk it.

A high-wing trainer will float on the wing if it is flipped over. your radio gear will stay dry, as long as the electronics are not located against the very bottom of the fuselge or the very top.

If you dunk it,

(1)pull the glo-plug and get the water out of the motor, then start the motor and let it run to dry out thoroughly.

(2)Check the foam around the tank and electronics-and if it is wet, remove it and dry it out on your workbench.

(3) if the foam around the receiver is wet, open the receiver case and set the receiver, battery pack, etc. in a warm dry place to dry before corrosion starts. The top of the hot water heater is a good bet.

Just don't leave the plane sitting around wet with the wing still in place. Pull the wing off and let air circulate in the fuselage to dry any moisture. This is true no matter HOW thoroughly sealed and waterproofed the plane is.

Topic B:
For easy changes from floats to wheels, make a T-strut for your front float mount. Snatch out the nose gear, replace with the T-strut, and the rear attach point for the floats is your existing main gear. see this link:
http://www.flyinglindy.homestead.com/skisandfloats.html