I agree- the furnace is the black hole of power. After our first outing and killing the battery on day 2 of a 3 day trip kinda left us worried. We bought a cheap genny (Honda wannabe) and it didn't do much. Installed a second battery and seems to have solved all problems.
2014 Stealth Evo 2850- "Woodstock"
2011 Toyota Tundra Rock Crawler TRD 5.7- "Clifford"
2013 Honda Accord Coupe V6 w/Track Pack- "Julia"
Just glad to get away