A couple of buddies and myself have a little routine that we think really helps. I honestly think it adds as much as 10 degrees of warmth, if not more. First we lay down some plastic tarps, the 6' x 8' ones you get from the hardware store. Then we add a layer of movers blankets. This really helps hold down the plastic tarps and keeps the ground a little softer & warmer, versus standing on the bare ground. We then stand up some of our screens that one of my buddies designed and made, these are 6' x 8' PVC walls that have 6' x 8' plastic tarps attached to them. This acts as a screen from intruding lights and drastically cuts down any breezes that may be around. We've made about 10 or 12 of these screens so we are able to make a good size enclosure around us if the need arises, depending on how many of us are viewing that evening. Then if the cold warrants it we fire up the propane heater(s) to give us that little bit of warmth that can take us from viewing for a couple of hours to viewing till the sun takes us home. During the normal viewing session, 5 -7 hours, we do not notice any frozen fingers and or toes that are normally associated with winter viewing sessions. But once the walls come down and we start to tear down our equipment the frozen fingers and toes have come as quickly as 10 - 15 minutes. And of course proper attire, lots of layers, is a necessity.
Nothing in education is so astonishing as the amount of ignorance it accumulates in the form of inert facts.