No. Considering that usable motorhomes are readily available for a few thousand dollars, and our standards for "poor" and "rich" are both quite high compared to that cost, they are not just for the rich. Indeed, fulltime motorhome living is quite popular among the economic homeless, those who do not have the resources and credit to buy a sticks and bricks, nor the income to pay rent in the places they prefer to live.
To live a middle class lifestyle, moving around in a motorhome, may or may not be more expense living that lifestyle in one place. That all depends on where that one place is, because I can rent four times the space of my motorhome for $400 a month or less in some places in the U.S., and in others I can't gat half that space for any less than $2000 a month, and you would not have RV living in those places either, unless squatting on public streets.