Never heard of RV Check; Carfax is only worth just about the value of the paper it's printed on. Many things will not show up, including owner performed repairs, and often even major things. I bought an H3 Hummer; Carfax was extremely clean; one owner, no accidents, regular maintenance performed by Chevy dealer...after owning awhile, I have found unmistakable evidence of a major right front damage/body work. Nothing about it on Carfax. I assume that RV Check would be similar.
Doubtful any of them would list previous owners, with privacy laws and such.