Bobby,
Best radio mounting method is to put all the electronics into a "tupperware" container.
If the ESC is waterproof, leave that out as it will probably generate SOME heat.
Goop works to glue the box in place. You will need 3 small holes:
push-pull for switch
antenna
rudder pushrod (& motor/battery wires if ESC is in box)
If the holes are tight fits, very little water will ever get in, even if
she goes to Davey Jones. Salt water is murder on everything electric/
electronic.
As green-boat sez, keep the weight low. My Lumba-Lumba was top heavy
and heeled over so much in a tight turn water came in the side windows.
Nice and fast is a straight line though!
Dave