help and options highly needed on single stage

You could use an industrial urethane that is designed to be applied with a roller. Rusteoleum makes some very durable paints and primers that are designed to be rolled on. You would have to wet sand and buff afterwards. When I say say durable I mean paint that is capable of surviving on an offshore oil rig.

I have a friend that owns a successful bodyshop and he says that all of their sanding primers are applied with a roller because it cuts down on fumes and overspray.