Definitely some great suggestions from others.I like this idea a lot! It's mobile for hauling into the shop for fills, garage to truck, truck to boat. It would protect the valves while on the boat if there was a little chop or wakes from other boats. Perfect solution for my situation, thanks for sharing!
My question for you is (as I'll be looking into solving the same problem) is how will you secure the tanks (in or out of a container) to the floor?