I talked to the guys at Tanks Inc. and they suggested that I use this rollover vent valve. It will vent the tank and also seal itself off in case of a rollever. I mounted it in the right rear stake pocket, ran the hose through the frame then to the tank. I'm not sure if moisture will be able to get in so I'll eventually get some covers for the opening.
Seal itself in case of a rollover, eh? Do me a big favor! Don't "field test" it, ok? Looks like a pretty slick setup! Ken