What type of generator

I'm planning on building an off-grid house in two years.  I plan to use a solar/wind combo with a propane generator for those periods where the system can't produce enought power.  I'd like to buy a generator, now, for occassional use, that I can move to the new house when it's built. Someone had  suggested that I get a liquid-cooled generator instead of an air-cooled generator since it might be running continously for extended periods.  The person who told me this said the air-cooled ones weren't intended to run for extended periods of time (days ?).  Is there any truth to this?  Since it might run for extended periods in the middle of the winter (in Canada), is the type of cooling really important when it's sub-zero outside?  Thx.