Lots of folks here have done a full-scale
renovation on their trailers. Mine was pretty crusty when I got it and while the cushions weren't totally dire, they were pretty musty. I soaked them one at a time in a bleach solution in my bathtub. The key is to have a way to dry them quickly after the soak because then you risk just inviting more mold.
Since I did this in the winter I didn't have the benefit of being able to stick them outside on a hot day. So I put them in a safe distance from my fireplace after experimenting unsuccessfully with sticking one in the dryer. Whoops, it chewed a little chunk out of that one, better not try that again!
Anyway, the bleach bath was a success - it de-stank the cushions so I was able to re-cover and re-use them all.