Use Velcro or Command strips for removable brackets. Usually good up to about 5 lbs. Not so good for TP holders and such that are subject to pulling.
For heavier or sturdier stuff, the basic technique is the same as any hollow wall, i.e. a "molly" type bolt or a hollow wall screw anchor. Interior RV walls are usually thin wallboard, either 1/8" or 3/16".
This article explains the various types of anchors. I like the spiral type for very thin walls.
http://www.popularmechanics.com/home/interior-projects/how-to/g1320/what-to-know-about-hollow-wall-anchors/