I have the F350, and it's not water proof at all. If you don't mind rebuilding when you take it in the water, mud or wet snow then all you need to do is protect your electrics. There are plenty of water resistant and even a few water proof servo's, there are also a few water proof ESCs, so really all you have to protect is your receiver. The truck will be fine as long as you rebuild and re-grease often, preferably after every time it's submerged.
Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return - Leonardo da Vinci