POLL-Paint or undercoat?

In the jeep world, the way we used to do the interior was sand/scuff the entire cab, wipe down with acetone (to degrease and prep) then rustoleum spray bomb primer. Let the primer set up, then roll three coats of Herculiner down... most of us never ran carpet, but even the guys that did said the herculiner made a big difference in heat and noise from the floorboards.. Never had a rust issue after that. And whatever herculiner was left over we would throw in a texture gun and spray the chassis with it. Worked great and wound up looking really nice afterwards... Just don't drive the car with no carpet and bare feet haha