I just remembered (because I saw the picture of the tanks, lol) that the maximum, in at least Florida and Texas which are the 2 states where I researched the systems, as long as each tank was not bigger than 119 gallons and were not interconnected you didn't need placards. If you were driving a company truck then you needed a CDL but if it was a personal truck then no CDL needed. In either of these scenarios a hazmat endorsement was not needed.
I remember we had to install 2 separate electric pumps, one to each tank, because the Texas DPS trooper told us if the tanks were connected by anything then it was considered one tank and it would need placards.
I used this setup flying helicopters in Florida when I worked for Universal Air and also while flying helicopters in Canyon Lake Texas. A google search might bring up the correct statutes.
I can't talk about other states though, it might be different.
I looked through my Part 135 hazmat training and found this link
http://www.fs.fed.us/t-d/fueltran/training/genawaretrng.pdfOn page 29 it mentions the less than 119 gallon tank thing. I'm sure if I kept looking I'd find more but last night I was researching which aircraft to buy and went to bed at 4:20 am and my girlfriend got upset. It's already 12:33 am and it's not in my best interest to do it again so, Goodnight to all !!
