If a used OTR semi was cost effective for hauling campers, people wouldn't use almost exclusively 1 ton pickups. That's where the bang for the buck is.
As far as making money at it. Numbers are easy to run. Consider full time haulers run about 100k miles a year and roughly half of that is dead heading.
At $1.35/mi loaded on 50k miles a year that's $67500 gross. Take out an average cost per mile of whatever you figure (25-50 cents) and there's no money in it.
I wouldn't get out of bed for $30k a year.
Your earning potential has to be pretty low to consider hauling campers as a career based on what has been posted here for compensation.
That said, I'm sure there are some mfgs that pay a bit more, because there are a few that seem to do ok financially with it (based on other forums I'm on), but unless you're really saavy and willing to Dooo it full time, you could make as much working the McDonalds drive through.