Supposedly if the tank is connected to the vehicle's engine, it's technically legal to bring 8 pesos/litre [$3/gallon] fuel across the border from Mexico. If the tank isn't connected, customs wil seize the diesel and maybe even the vehicle. Even if it is connected, customs may give you a hard time. Supposedly a driver can earn $100 a trip running diesel in border areas but each border crossing takes an hour or so . . .
It's a whole lot more cost effective to just electrify the #@!%&*! tractors and fields.
A 1/2 mile long wire 10 - 20 feet above the ground only needs to be on one end of a quarter square. A fast discharge battery can be relatively small as the tractor only needs to go one mile for the round trip back to the wire. A small ICE or battery trailer could be used to relocate the tractor any distance.
As agriculture become more automated there won't be any reason for anyone to be in the tractor so no one will get bored as the tractor lingers for a minute or so charging up at the wire.
If someone wants to ride in the tractor they can bring other work to do during recharge.
Bret Cahill