Looking at new Class C but there is a seat issue

If it's just the seat depth to the seatback, a cushion between your back and the seat back might be all you need. (Pedal extensions, as others have mentioned, are also a reasonable option.)

I don't think remounting the factory seat farther forward is practical. Putting in an aftermarket seat is pretty straightforward, though; basically it's just four bolts to attach the base to the vehicle.