Can I hang cabinets and shelves?

Any RV that is built with wood construction, i.e. wood studs is easy to retrofit. To install cabinets, you'll need a nailing strip or two in the back of the cabinet. If you look at most wall hung RV cabinets, you'll find the uppers are usually fastened into the ceiling joists, as well. Screws and glue are a better alternative to a common nail.

As has been posted, the FEMA trailers are not set up for camping and a good bit of retrofit is necessary to make one suitable for anything but full hookup camping.