They are rare, and usually for chassis problems. Most of the platforms have been mature for a long time, so it has mostly been the Sprinter getting recalls and warranty extensions. I expect to see more, now that we have two new vehicles being used as C motorhome chassis.
NHTSA concerns are focused on vehicle safety issues, would cover defects in safety equipment in the house, or structural problems like things falling when the vehicle is in motion.
Safety or standards compliance issues associated with the use of the house as a house fall under other authorities, so we get consumer product recalls for things like defective microwaves and refrigerators that catch fire. These usually fall back to the component manufacturer.
