OP.
I wouldn't recommend idling your truck to use the AC/heat while you are in an enclosed area in the back of your truck. As well, your truck is probably not intended to idle for long periods of time but more importantly, exhaust build up within the canopy could potentially be a life threatening issue. I even believe the canopy I have has a disclaimer sticker attached indicating not to be in there when the truck is running... or something to that effect. Sure, going down the road with the truck running is different than idling as when moving, air is getting into the truck/canopy area... not so when idling.
The truck bed will be the least insulated, so make sure to insulate that well. Then use a backpacking style sleeping bag rated for the cold of the outside air.
To cool when in the summer, a canopy with windows for side to side screened ventilation along with a battery operated fan should help a lot.
