We installed 120vac/USB outlets in two locations in the bedroom and two locations in the main cabin. No difference from doing it in your sticks n bricks. Use the box already installed and just discard/save the old outlet. If you need/want a different box, those plastic "new work" boxes work well.
Careful tagging out sources. 'trons come from all over in these rigs.
We also replaced all but one of the 12vdc power outlets with twin USB outlets. That works out to two in the bedroom, two in the main cabin and two on the dash. Didn't change one because.......you never know.
Fair Winds and Following Seas