Prime the walls of the camper with a high quality primer and paint them a light color like white, ivory or a pale pastel like yellow.
Take the hardware off of kitchen, bathroom and storage cabinets. Clean it well, prime and paint it white.
Replace old knobs and hardware with new hardware and knobs.
Remove any carpeting and carpet padding. Cut it into manageable pieces with a sharp utility knife and dispose of it.
Sweep and vacuum the floors and install laminate wood. Choose a laminate wood that snaps together easily and has a large color variation so it hides dirt well. Purchase at least two extra boxes so you can easily replace damaged sections of the floor over time.
Replace upholstered cushions with new cushions. Use patio cushions for a budget sensible alternative to having cushions customized to your needs. Save even more and wrap the cushions in new fabric, securing them in place with adhesive hook and loop tape for a no sew reupholstery option.
Replace of old curtains. Hang new valances over sheers for a quick window redo.