I live in a Coastal area with salt air and in the winter they salt the crap out of the roads. I am a firm believer in undercoating our cars and truck. Was not sure about the MH. However, we do plan on doing some winter travel and the moist salty air wont be any good for metal on the RV. So I did do the chassis (inside the doors, rocker panels, engine mounts and the frame under the coach. Also did the axle, battery box, propane tanks etc. If work ever needs to be done on any of these areas, it is not tar or oil based and can easily be cleaned off.
2015 Coachmen Prism 24J MBS