The problems with trailers are many, not the least of which is the heating system.
When you access the ducting, you will find it to be full of holes, the crawl space will be heated and cooled much better than your house. To hamper access to everything, the manufacturer thoughtfully laid a sheet of r13 on top of the trailer rails before setting the box of the house on top of it. While the insulation isn't doing much, it is something, and you'll riddle it with holes during your replacement of the ducting. Be prepared to reinsulate the underside of the house.
While you're running new ducts, you may want to think about installing a return air branch as well, rather than relying on the convective transfer system that doesn't work well.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!