I have no knowledge specific to your RV.
If its in-warranty, I'd take it back to the dealer. It's not sufficient that the satellite input can pass an RF-signal (if indeed it can). It has to pass DC power as well to power the LNB. If you have a volt meter, read the voltage on the "sat-in" jack on your receiver; then connect it to that coax and see if that same voltage is still there outside. (My guess is that it won't be.)
If it does work with a DVD player, that probably means that there is a splitter installed in the satellite wire, which is a no-no. It wouldn't be so uncommon to have one on the cable-in wire, which would explain why that wire doesn't work either.