Long term car storage.

Hi all, Boeing is sending me to Australia for at least a year but most likely two years and I need to find a place to store my '74 Swinger and 2011 Chrysler 200 conv. A buddy of mine at work said I could store both of them in his barn for $150 a month but then backed today saying he was not able to due to flooding and very soft ground. I have looked online for long term storage but most places here want $200 per auto and that is outside storage which in my mind is a buffet for parts thieves. Has anyone had to store their cars for a long period of time and if you did where and how did it work out? I live in Woodinville, WA so any place around Seattle is good. Another thing is the Dart is not running so I will need to tow it. Thanks, Edward