I seriously believe that you have a trailer, inwhich a human corpse decomposed.

Metal will not absorb the smell. However, EVERYTHING else will!

Strip the trailer - ENTIRELY of its TOTAL contents - leaving only the bare metal wall. Scrub the aluminum wall first with ammonia (don't worry about the aluminum warnings regarding ammonia - you WANT it to oxidize and release the fumes and perhaps any remaining spririt of the diceased.) Then scrub again with chlorin bleach. Now, rebuild the trailer and fill the vacant spaces with sawdust, borax, and baking soda.

Sincerely,
Gargoyle

It worked well for my neighbors and their Mercedes which had a double suicide in the garage on a hot summer week.