Hi Grant,
A radio box is for boats with an internal combustion engine, these need air and the boat can't be taped shut, so a little water will always find it's way into the hull, messing with the electronics.
A fast electric is taped shut, so it is basically watertight.
In my fast electrics I have no waterproofed ESC, servo, or receiver, the boats are watertight during the run.
A piece of kitchen towel on the deepest point in the hull absorbs the few drops that find their way inside via the stuffing tube.
With a floodchamber, you don't even have room for a radio box, as it'll upset the balance, rendering the floodchamber useless.
I added a picture of the internals of my Arowana, including the slits in the top of the floodchamber; the extension in the hull is the floodchamber top and side wall, against it you see the ESC and battery.
On the right side there's only the servo and the receiver, tucked away under the edge about where the red arrow point at,
all heavy stuff sits left of the center line, a must for a functioning floodchamber.
Regards, Jan.