There are several decent quality brands, so just pick one. Some of the better knowns are Pressure Pro, TST, TireTrakker, TireMinder, and EezeTire.
People will rant about replaceable batteries or not, temperature reporting or not, and flow-thru sensors or not, but those are all nits in my opinion. Not of any real significance in the scheme of things and not worth agonizing over either. I would be more concerned about the the readability of the display and the ease of mounting it in my particular RV.
Here is a previous topic on TPMS choices, and I think there have been some later ones that a Search would probably turn up:
http://www.rvforum.net/SMF_forum/index.php?topic=64310.0