I can imagine a propane unit running off 40-100# bottles, but I haven't seen a setup like that.
I just went through this, we just had a nice 7 day power out from the Halloween noreaster. I just got a 16k propane-fired generator in the middle of this last storm. it is much larger than I want but the price was right.
I was told I would need minimum 4 #100 tanks to use that way and I wouldn't be happy with results. they recommended at least 2 120Gal tanks or larger for long duration storms. it'll just freeze up a single or dual setup 100#.
The thing with propane is it takes A LOT to get it setup, these are NOT portable in any sense. I couldn't get mine setup on a temporary basis as the parts are all trade-only sales. no plumbers or gen tech's are available in the middle of a major blackout. Also, you need to have enough reserve to outlast the black-out. I was told minimum 1 week for a delivery if I bought a 325 or 500gal tank in the middle of our noreaster last week. We ended up just using a 7k gas unit (much easier to acquire fuel).
That being said, I am going to get mine installed in the spring after we do some construction work, bury a 500gal tank and have peace of mind. however I am NOT going to run my 24x7 like many around here did. they're burning $75-100 of propane a day that way. I will have mine running for heavy loads like laundry, showering, etc. during the day when our demand is quite light I will run on a 5k 24 or 36v inverter with a large bank of batteries. This will run the furnace, lights, fridge, etc that do not need the full output of the generator.