Install a 12 plug in the camper somewhere and use a 12volt fan. THe endless breeze are good, and HERC's option to.
They draw about 2-3 amps so will use 15 or so amps in 8 hours, The furnace will use 4 or more when running, so you may consume as much 35-0 amps overnight with these two sources. A stock battery will get pretty depleted, unless you are carefull and monitor closely.
2007 Chevy 2500HD Classic LBZ Duramax/Allison (Stock)
2005 Bigfoot 1500C8.2 AWESOME