Peppermint Oil

• Peppermint has a strong smell that can help freshen up a stale room. Dip cotton balls into some peppermint oil and set them around the camper in locations prone to musty smells such as couch cushions and in closets. The cotton balls will disperse the smell of peppermint without letting it leak all over your floor. While the oil smells sweet, it doesn't offer any real food source to pests, so bugs aren't a concern when using it. Remove the cotton balls after the musty smell dissipates.
  
  

Potpourri Baskets

• Setting up decorative baskets of potpourri helps freshen up the smell of your camper while adding a tasteful decoration. Place one large basket of potpourri in the largest part of the camper, or set smaller baskets strategically throughout the camper. Potpourri takes a while to work its magic, so be patient and let it sit out for a few hours to clear the lingering unpleasant odor. Store the potpourri baskets safely in a cabinet before you take off in the camper, though, or you will have a big mess to clean up afterward.
  
  

Dryer Sheets

• Dryer sheets are inconspicuous and flexible, making them an ideal weapon in the fight against musty odors. Place a dryer sheet in closets, under cushions and in the bathroom of your camper. Wipe your fabrics with the dryer sheets as well to transfer some of the smell to your neglected linens. Replace the spent dryer sheets after a week so the new ones can keep working their magic and preventing the recurrence of musty odors.
  
  

Food

• The smell of freshly baked bread or cookies quickly fills your house with an enticing aroma. Setting your dishes in the camper to cool will spread the smell through the musty rooms and make it smell much more pleasant. Be careful, though, because sometimes the smells of the camper can infect your food. If you have a minor odor problem, your food should be fine, but if the smell of the camper is overpowering, you should refrain from setting food in there until you dilute the smell through other means.