Hi,Ken, any auto electrician should be able to test the van to estimate the Max load of that vans system or you could run the air con from a second battery as like a motor home but ask an expert first
The van is 12v, alternator is 40Amp:
You have a portable generator capable of up-to: 480Watts constant power
Factor in say 80W for all ancillaries operating...
400W to play with

Find a compact car air conditioner that can run off that much...and your done...
or just pop in a bigger alternator

I do know of fridge/freezer rascals with a massive thingy on the roof...so I imagine there is enough power, you just need to find a suitable unit.
oh...and send that weather over here...it's bloody freezing!, lol