I installed a brand new 175 litre three way as per the book and I'll never have another gas fridge for one simple reason - during high wind conditions, the pilot light keeps blowing out when the bus is sideways to the wind on the fridge side! And another thing (OK, I lied), they just do not work as efficiently as compressors chewing through the gas while the compressor has reached temperature and shut down long ago.
But (and there is always a but), due to your financial situation consider this:
If you get the heater and travel south in winter, you will be going against the traffic
with vastly better camp site options, the fridge will not be as great a concern and you will keep warm outside in the daytime because the fishing is better in the wintertime. 
dawg (who doesn't follow his own good advice sometimes - errr, make that most of the time
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