I don't think the numbers you posted are impossible to achieve, but comparing camper rentals to home rentals may be a mistake. The camper rental business will be way more labor intensive even without repairs. Whether you are renting them long term or short term you will have to deal with higher turnover than home rentals. Even if the campers are kept in good condition, their value will depreciate at a faster rate than a home, with zero chance at market appreciation.
I won't wade into the different tax implications, but they should be considered.
That being said, if you are in the right area and flexible enough to find a niche (example: snowbirds, tourism, following natural disasters, and/or large construction projects) it could be a good cash flow business.