best way to warm a minivan ?

[Speedy]

I strongly second this:

freeradical wrote:
Make sure you have a foam pad to sleep on.

Easy to keep warm topside with lots of sleeping bags/blankets. But most any bag/blanket will compress in the night, even on a mattress, and you will get cold. But a foam pad will insulate you quite well. I've used sleeping bags and a good pad down to -20F.