Here, take a look how I did mine:
http://www.gmsquarebody.com/forum/showpost.php?p=303329&postcount=34
From the factory service manual:
You must be registered for see images attach
The switch:
You must be registered for see images attach
You can see mine here again in black. After a few camping trips, the enclosure has cracked a bit more (was already a bit broken) but still works fine, and works well as a boot warmer too! And also serves as a rear defogger (but is weak).
You must be registered for see images attach
There are two type of auxiliary heaters for the burb (and also the blazer, but I'm not too familiar with them.) They are both very similar, and function the same way. The first is what you would get if you ordered it from the factory with RPO code: C36. The second is a kit you could purchase from the dealer to install a rear heater in a burb (or blazer?) that didn't come with a rear heater originally. The only difference I know of is the switch: the factory-equipment version just has high and low settings, while the add-on kit has high, med, low. Also, the add-on kit comes with just 5/8 and 3/4" heater hose, and does NOT include the metal pipes from C36 RPO code. From the factory there are two sections of send/return metal pipes that are connected with heater hose that mount to the frame rails. Strangely, the power/ground wires for the fan also run under the vehicle.
Any other questions about this just let me know, I have gone through exactly what you probably will have to do and can lend my knowledge. Did your vehicle have a rear heater already? Or are you trying to retrofit? You will need the heater enclosure + fan, the heater core (which is still made), the dash switch with wiring and vacuum line, and the heater control valve which splits coolant flow to the rear and front when selected.
Here are some pictures of that GM dealer add-on heater kit, it is very similar except for the switch and piping, and shows more of the pieces in detail:
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach