I would suggest that you look at a Rinnai Energysaver. There are many of them in your neighborhood.

Thanks Jackfre, I will check out Rinnai Heaters.

Why not just use a small oil furnace? They're durable, easy to find on craigslist etc., can be run from a 55 gallon drum (if used only occasionally) and can be found for less than a few hundred dollars in much of the adirondacks. They'll likely cost substantially less to operate than propane and, if you don't want to have a fuel truck deliver, can be filled w/ off-road (or on road, but then you pay the road tax) diesel (same as #2 heating oil)

How about a heat pump since you won't be there in very cold weather?

I don't think a heat pump would work. After October 1st the temp can go below 40-45 degrees any night and my understanding is that heat pumps become very inefficient below that temp. As for using oil, I don't have a chimney and don't want to go to the expense to have one built. Both good ideas but I don't think they are an option for me.

http://www.mitsubishipro.com/media/226460/h2i_brochure.pdf

http://www.youtube.com/watch?v=59VCjwEWGQQ

If you don't have an exhaust, how do you plan on using propane?

A high efficiency HP works just fine below freezing. Many of the mini-splits work down into the teens.

A heat pump should work, but the Rinnai is a less expensive solution for heating only. The heat pump would provide for cooling and dehumidification in the summer on the rare hot days.