A lot of class "B"s have a furnace that won't last the night on batteries, especially anything made before 2012, when bigger battery banks were not common and Truma wasn't in the market yet.
As an alternative, one could use a Buddy heater, or look at a vented Platinum Cat system. The Plat Cat uses 1-3 amps compared to the 7-12 amps a normal furnace tears through.
PW Excels are decent vans. They had a very long manufacturing run, all the way to 2015, pretty much using the same fiberglass body. What killed the model was the fact that Ford killed the Econoline van (not the cutaway, but the van.) The only downside is that I read about wiring issues.