Easiest way would be to use the Dometic ducted install kit- around $100. That would give you a thermostat and control box that is plug and play. Then you can either just remove the existing box and knobs and cover the holes, or leave them in place but not functional.
FWIW, Dometic makes that air distribution box for wall thermostat applications- they just have a sticker covering the holes.
-- Chris Bryant