If it is legal in your home state, the others can not tell you no.
California has some of the most restrictive laws - and most gas auxiliary tanks installed after 2005 are not allowed. Diesel tanks are a little less restrictive, because they do not need to meet the less than 20 grams fuel loss per day - it can happen when gasoline evaporates and leaves the tank.
From what I hear, gravity flow tanks are not allowed. This is because in a accident, it would be possible to separate the tank from the pickup bed, and fuel line would break and dump a lot of fuel quickly. Or if the pickup overturns, it might drain fuel from the tank or it's connections. Also there might be a possibility that the gravity flow might overfill the main tank.
You do not have these problems, as you have a transfer pump, solenoid valve to stop flow when the pump is not running, and probably something to prevent the main tank from filling from the Aux tank when it is already full.
So I say keep using it. IN a gas truck, I would say if the model year where newer than say 2005 it might not pass EPA's stricter regulations.
Fred.
PS: You can check the laws at
Transferflow.com They also sell larger capacity diesel tanks for all the major brand trucks.
Money can't buy happiness but somehow it's more comfortable to cry in a
Porsche or Country Coach!
If there's a WILL, I want to be in it!
I havn't been everywhere, but it's on my list.
Kangen.com Alkaline waterEscapees.com