I guess having a couple of forklifts on a trailer smooths out the ride.
Our DOT administrator is JJ keller so this was the advice they came up with for our legal dept.
In the old days we asked the Highway Patrol about how many tanks and they told us to call the DOT.
The rule talks about the potential weight of the fuel the tank could hold plus the tank, so it would depend on tank size and steel or aluminum.
The interpertation of the rules for the chain down technique (how many per) has been a topic with different answers depending on who you talk to.