Depending on the RV some have enclosed underbellies and some of those have a heat vent going to them to help keep the bottom warm they can be used to the lot 20's but since you are using a Mr Buddy it will not heat the underside... so the coldest I would use the RV would be if the overnight low did not go below 28 and the daytime highs were above freezing.
2004 Chev Silverado Duramax optioned past the max. 2009 Jayco Eagle 308 RLS 765 watts of solar, 6-6 volt batteries (696 amp hour), 2000 watt (4000 surge) whole house inverter.
140 days boondocking in 2016
211/2015, 196/14, 247/13, 193/12