Being as you're hurting for funds, the $600 RV might be the way to go. After all, all you have to is use it for a month (even if you don't use it anymore) and it's paid for itself. You can live in it for at least for another three months without a working furnace.
After you buy it, you'll have time to evaluate it a little further to see if it's worth a refrigerator. Buy a dorm unit used and put that in there. The main thing is that it has to be able to move on its own so the engine and tranny have to work. And check the tires that they're good enough to get it to a camping place.
And find a camping place that will let you in with it before you buy it.
I like to see that you're working and trying to find a way to save some money but I wouldn't figure that one of these will be a long term solution to your housing needs, but should work for the summer months.
Bill