If you're using the stock AM radio that comes with it that is likely the source of the control problem. Many others have had this same issue without anything getting wet or any interference. This can be solved by replacing the stock radio with at least a quality FM radio system.

If you use a receiver pack you plug it into the BATT slot of your receiver. For your ESC plug you remove the middle red wire from the plug by lifting a tab on the plug and pulling it out and tying it back. This disables the BEC. It can simply be re-inserted in the plug if you want to use the BEC again.

The receiver pack powers your receiver and steering servo. The BEC function of your ESC steps the voltage from your main batteries down to 6V and uses this to power the receiver and steering servo. With input voltages too large (more than 12 cells) this functionality will not work properly which is why you need to use a receiver pack. Also you are more prone to radio glitches using the BEC.

Hope this helps.

Greg