Its been over ten years since I dug into it. Several sates have laws regarding carrying hazardous materials outside the vehicle body. Some states just listed gasoline, others said any hazardous materials, So one should check their local, and state laws. Many of these racks for holding the 5 gal mil gas cans, scare me. What prompted it, was on a 4wd forum, and a member had a 5 gal can fall off, and he got a ticket for having a storage container outside the vehicles body. Then another member admitted that he had a rack break, and lost a can (did not know it happened until he got to his destination ). Luckily both cans were empty at the time. The whole thread scared me, seeing how clueless so many folks are, mostly when the discussion turned to securing gas, and esp propane tanks. Had at least one person that insisted propane tanks were built so they could roll around the back of a pickup bed.
My trailer has 4 metal loops welded on the floor, to holds straps to strap oxygen tanks horizontally to the floor. Gaseous cylinders I have a few holes in the front corner that I attach some screw eyes to hold straps to secure the cylinders, including propane. For my medical oxygen, I have a rack that holds 8 cylinders, and completely encloses them. Probably not right, but I just throw the whole rack inside the back of the minivan, and run down to exchange them.
Randy, that is a great design, I like how things well thought out, yet simple in design.