David,

Thanks for the info.  I took a look at Dave Garth's heater installation.  
It looks pretty good!!!  I think that is must be a catalytic heater, 
which, if I'm not mistaken, doesn't need a significant amount of 12 volt 
power.  I was thinking of installing a catalytic heater, but I have a 15 
month old, and I'm concerned that he might burn himself on an exposed 
heater like this.  The furnace that I'm talking about is a forced air 
heater, not unlike the gas heaters that some people have.  Also the 
outside vent on these things is about 3 inches wide by 7 inches tall.  
Seems like a relatively small hole in the side of the van.  At least it 
is not 9 inches by 9 inches.  The vent is also looks like a chrome plated 
die cast metal thing, not one of those cheap looking motor home vents.  

Thanks for the response.  
John