Do you have a slide awning?? Maybe some funky stuff on the seals?? You might try an appropriate cleaner. Does the smell come inside the trailer or just outside? If you have a slide awning, you may want to try a good cleaning on both sides - reaching the underside of that awning is a challenge, but something like a soft long-handled car wash brush should help. BTW, when you rinse, especially the underside of the awning, use as gentle a spray as possible so it doesn't seep inside and allow to dry thoroughly.