Heater upgrades from std. heater for 'burbs and panels in cold climates???

[Chuck78]

Okay, aside from the fact that I've never had any barn door weatherstripping for my 62 GMC panel, the standard "recirculating" heater just does not seem to be cutting it... When I had the back door stuffed with rags, and a full load of cargo in the back (thus greatly reducing the heated space), I was barely able to keep it comfortable on the Thanskgiving day drive an hour on the freeway.
Not sure if I am missing something, but my standard heater just sucks in one side and blows out the other, or else blows through the defrost ducts. Are there supposed to be other ducts hooked up to this style of heater, and where do the vents go on the deluxe heaters? In the GMC dash, or mounting under the dash attaching to the bottom of the dash?

I don't really like the look of the deluxe heaters at all (under the hood), and am thinking there has to be a better way to go. I read in one thread that there was a dealer installed option for an auxiliary Suburban rear heater. I am thinking i need something more... the heater in my 89 Suburban (a good 20" deeper cargo area) has some serious output, and I want something that heats this large area that well... I have wondered about swapping that in, but that would mean butchering the firewall up for the swap. Then I thought about 67-72 heaters, an maybe hoped the SUburban models might have had something larger.
Maybe I should just swap the brand new 180 degree stat for a 190 degree stat????
At any rate, I think I'd like a ducted heater, and my only other thoughts were to maybe get a vintage air system or similar, designed for a retrofit to our trucks, and just use the heater box and not get the A/C compressor/filter/drier/lines. Then I am still left wondering, is this system designed just with the pickup truck cab in mind????? My 7-1/2 foot panel would be the equivalent of 4 pickup cabs worth of space to heat!

I'm sure other northern guys with panels and burbs have had this problem, so I'm hoping for some insight. My 275,000 mile 1989 Suburban is a GREAT solid running truck chassis (original engine, TBI 350's are awesome), but the body and body related electronics are all totally falling apart, driving the 62 GMC most days that there's not snow or salt on the roads.

HELP!

-Chuck in Ohio