My next new van will have an Espar heater which is advertised elsewhere on EO. At about $1300 installed, it's a good value for the money and an efficient way to heat the van with a unit about the size of two cartons of cigarettes.
I keep cool with a FanTastic fan at about $220, you install. Thermostatically controlled, it keeps the air moving and we sleep comfortably in our well insulated van.
You should get a Carbon Monoxide detecter at Home Depot, Lowes et el, not only for your fumes but for the others that are idleing and sharing their fumes and gases with you. I almost woke up dead once so I think the $40 is money well spent.
I have a 534,000 mile gas van that I have idled many hours at a time in its five year life. The engine still runs tight and only burns 1/2 quart every 5000 miles at which time I change the oil.
I think you should consider one or two deep cycle batteries, isolated from your starting battery. You'll be able to then use all your aux eqpt like Qualcomm, TV, DVD player, computer, work/reading lights without fear of not starting in the morning.
Terry