TC wrote;    
>>But in going over some of the mountian pass's in sub-zero blowing snow
 >>conditions  the snow would melt in the center of the windshield & freeze
>>around  3-4" of
>>edges  of the windows making visibility a bit tricky we were making lots of
>>heat
>>but the design of the heater ducts does not realy lend to covering the
>>entire windshield ...

Why not add a small fan to the dash?  The kind of swivelling 12v fan you see in big trucks and RV's.  You could use the fan to direct extra air to the windshield in the winter and toward the passengers in the summer.
Also make sure that all the levers, cables and flaps are working correctly on your heater/defroster controls.  
George,
'85 Wesrfalia