Haz,
Here is a link to fuel comparisons:
http://www.propanecarbs.com/propane.htmlWhen we farmed we had three straight trucks, and one was LP. Over the three years I tracked it, the LP (Chev 396) was cheaper than the IH (39?) and higher than the Ford (360) in terms of fuel costs. However, two important points: 1. The Chev and the IH both had boxes that held 375 bushels and the Ford only held 250; and 2. The Chev (LP fueled) was the only one that was tarped, so it ran out down the road at 60 mph all the time, while the other two were limited to 40 mph when loaded (have their road time).
We always figured it was a wash in fuel costs between the two bigger trucks. However, for a home generator you would save road taxes by buying LP rather than purchasing gas or diesel at the pumps. I had 1,000 gallon tanks by the grain dryer where I filled, and I paid road taxes annually based off miles driven.
You won't have issues with temperatures down there, but up here the LP truck needed to be preheated in cold weather to start. When temps got in the teens and lower it the fuel would not vaporize if the engine was not warm.