wondering if I need dot numbers.

I don't know your exact application, so I may be talking out my butt.

could you carry a concentrated powdered trichlor and add it on site?

what about setting up your system as a feeder tank instead of a carrier tank - you could haul virtually empty, but you would have to have water hook up on site for your feeder tank and the time it would take for it to get ahead of you so to speak.