There are some features you should look for:
1. MUST HAVE: S.A.M.E alert system
...Specific Area Message Emergency (or some such...) This listens for messages that affect your local area and sets off a siren and plays out the message from the NWS for you. I would not own a weather radio without this feature. The others will give you weather info but these wake you up in the middle of the night with lifesaving info and the others will let you sleep right through an F5 tornado! Also if you set the SAME code to 999999 it will respond to any alert it hears. Can be annoying. You have to tune to the local weather station each time you move. You can look them up in a book or just tune to the loudest/best signal.
2. Get the kind that require a 12 vdc wall-wart power supply. Then run the radio off the 12 vdc system of the RV. The 12 vdc is always there, but 120 ac may not be.
3. I also like ones that have the external antenna port. This can be fed from your roof top antenna. The weather bands are near analog channel 5 so that antenna works great. Be sure not to use this set up when hooked to cable! The built in antenna on mine has always been sufficient for me. My RV has fiberglass skin. An aluminum skinned rig maybe not.
My radio is a Midland which also doubles as an AM/FM clock radio. But Midland, Oregon Scientific, Radio Shack and others are also good. I send people to Radio Shack because I know they are always in stock and close by and some managers are smart enough to show you how to use the radio.