Hi buddy i transport dive tanks alot and having a commercial truck for diving, the only way to transpot them is standing up against the cab. they should be tied or supported so that they cannot move. If you lay them down and have to hit the brakes really hard they will move and gear will come up against them, if you get rearended they will also move. take 2 pieces of plywood and make a rack about 5 feet long get a jigsaw and cut out the holes for the tanks, holes about 4 inches apart, then cut some 2x4 and insert between the 2 pieces if plywood on edge and also on the bottom. If you have a truck and must carry them lying down be carefull always stand up tanks when transporting.....and you also might want to check on the quantity of tanks allowed by your state cause after a certain amount you need the 1002 dangerous goods placard for hazourdous goods, bottom line if you can at all stnd them up, your valves will thank you......i know cause i been carry tanks everyday for 14 years....