We camp at Yosemite once a year during Thanksgiving. We've been using the Buddy Heat for years to keep the coach at about 58-60 degrees during the day. That doesn't sound like much, but ours is a 40' full wall slide coach. I leave it on low in the center of the coach. It will run about 5-6 hours on the green bottles. It's just enough to keep the walls, cabinets and furniture warm, so that you're not trying to reheat the interior at night.
At night we use our coach heat. In the past, we've moved the Buddy Heat closer to the bedroom and ran it all night and it worked well. As one poster noted, you can refill the green bottles with an inexpensive valve from Harbor Freight.