Honda 2000
The propane connection seems easy enough, if buying it to use both, i think if you hook up the propane and run it that way first, you don't have to adjust anything. If you use gas first you have to adjust something. I THINK....
In FL - run window shaker AC, fridge, chest freezer, fan, TV on mine. Did a week w/o power on about 10-12 gallons of gas - ran about 8 hrs per gallon and I was working, so it wasn't on the whole time. Wife would fire it up when she got home and I'd top it off at about 10 PM and then at 6 AM when I left for work so wife didn't have to.
If I was gonna do it again, would either buy one with propane adapter or put one on. Did math a while back and would get about 24 hrs off a $20/15# BBQ propane tank. Would get the same burn time on about 3-3.5 gallons of gas, so not as fuel efficient but clean and easy.
I do run mine every couple of months to keep fuel fresh. And use fuel treatments... It is about 10-15 yrs old.
We bought my folks the knockoff version from Harbor Freight and it sits in the original box, haven't needed it yet. That one is about 8-10 yrs old. Go figure.