John Dziadecki inquires about heat, among other things.  My take is that
electrical solutions are a joke.  For proof, sit in the car some cold morning
with a 120v hair dryer on low -- nothing that runs on 12v will give you more,
most will give you a lot less -- and see how long it takes to make a 
difference.  First thing to try is make sure your heater boxes aren't leaking.
The flapper valves are a weak point; you could consider removing them and
putting a good insulated duct from the heater box direct to the pipe to the
interior, and just leave the heat on full that way all winter.  Speaking of
the pipe to the interior, you could replace or enhance the insulation on that
as well.

Other writers on this list have mentioned insulating the walls, which I may
try both for temperature control and for noise.

Re mufflers, JC Whitney has a bus muffler for about $70 that bolts right to
the heater boxes, no J tube no nothin'.  Not the quietest or best looking
piece, but it worked for my Vanagon.  They also have a $70 inline blower that
helps move warm air from engine to interior.  Noisy! but it helps.
B.