I just went through this transporting a game to MGC in the back of my F-150. It's about a two hour drive. It rained all the way there and snowed/rained on the way back. What I did was:

Shrink wrap entire game.
Put on top of a tarp and a couple of 2x4s to keep it off of the bed in case the bed takes on rain water.
Pull the tarp up on the sides and bungee it to secure it.
Put a tarp (the thicker the better) on top, secure tight with ratcheting straps around the game.
Then I put a couple more ratcheting straps across the corners of the truck bed over the game for good measure.

Now, this is a pain in the ass, but I didn't have any issues with water.
In the past, I've also removed the head, but removing and reattaching the head twice for a show is also a pain in the ass.