I have a 22" TV with built-in DVD player that I mounted as a 2nd TV (in the bedroom). The nice things about the built-in DVD player: it doesn't take up any additional space, and if I can't get a TV signal, I can always watch a DVD. Does your X18D have a TV antennae? If not, you'll need one of those, too. I'd stay away from those flat ones that "mount anywhere". Their range is very limited. I have a power-boost HDTV rabbit ears that I use at home (too cheap to by cable TV), and use to take camping, too. Its range is better than the flat panel, but not nearly as good as the one on my new Eagle.
I also use the Lego-style blocks for leveling, tongue jack, and stabilizers. You can pick up a 10-pack with storage bag for about $29 when Camping World has them on sale. Very handy, and much lighter in weight than wood!
2013 Eagle 266RKS
2011 Ford F-150 w/3.5L Ecoboost & H.D. Tow Package