Acetylene stands up, Oxygen lays down. If they can see my O2 tank then they can give me a summons but nobody can see it as it is hidden. It don't matter in Tennessee(Actually it does but nobody enforces it). I see tons of idi....guys with tanks in there pickup truck beds, utility beds, all regulators in place, ratchet strap holding them down. For my tanks to come out they're going to have a lot more to worry about that a couple of tanks, namely 11,000 pounds of truck flying around thru the air! LoL! I've bought clamshell caps for mine, have had them for years and wonder as I drive down the highway why I even bothered when I see other "rigs".
Been clean up thru Illinois, Wisconsin, both sides of Ohio, Pennsylvania, New York, Kentucky, Alabama, North Carolina nary a problem. Other than Komifornia I don't see to many states as hard nosed as N.Y.
Get my bed done though and it won't matter as all will be standing up. The safety caps though as far as I have read are supposed to be legal for transport.