The owner is forbidding idling because it's expensive and there's already not much margin.
I have a Big Buddy heater, that helps. You must have the windows open about an inch or so if you use one of these things, but it does allow me to keep warm in my van without idling.
The other reason for not idling could be... Idling the newer Diesels leads to engine problems in short order. EGR's, DPF's, and other parts of the newer gen. diesels don't handle the idling with out gumming up stuff. And it's become too expensive to burn the fuel.
I too have heard of folks using the Buddy Heaters and there is more than one size.
I use a 12v electric blanket and a good sleeping bag, a few other blankets and I'm good to go.
The blanket heats for 30-45 minutes which seems to do the trick. I run a little differently than most, so this works for me. If I had to stay out like most, I'd go the Buddy route, too.
A/C in the summer is handled by my confabulation of a plastic ice box rigged up with a fan to blow air through the ice and it seems to do pretty well, even this last summer when it was killer hot. You can also buy them for inserts into a camping ice chest at most truck stops or online. I just happened to have the pieces parts and made my own.
I guess the point is, it depends on the type of running you do that drives the need for the equipment.