Set up your tent trailer. Open all the windows and doors, allowing it to dry out completely. Let it air out for about a week and sometimes that will be enough to get rid of the musty smell.
Diffuse some cinnamon oil. This is a strong and safe disinfectant that will help eliminate the musty odors. Place a small bottle of cinnamon oil on the table and use diffusing reeds to send fragrance throughout the trailer. Make sure the tent trailer is completely closed up to get the best benefits from the cinnamon oil.
Fill a bucket with hot water and some color-safe bleach. Scrub the fabric surfaces on the outside of your tent trailer to clean away any mold or mildew that may be causing your musty smell. Clean the canvas on a sunny, breezy day to make sure the fabric will dry as quickly as possible.
Prevent future problems by applying a tent trailer waterproofing solution, sold at camper retailers, to keep the fabric from absorbing moisture and that musty smell.
Remove any mold or mildew from the non-fabric portions of the tent trailer using a mixture of one part vinegar and three parts water. Scrub these surfaces and dry well with a towel.
