I had a Hawkins HMC that had the CAT 3208. The Onan generator had been an LP fueled unit but the previous owner had converted it to run on gasoline. He was a national drag racer and found it more convenient to have the genset run on gasoline, which he could refill more easily vs. running out of propane and no way to refill while at the track.
It was a very clean conversion and gas tank install that worked great for the years we owned it.
Paul & Sandy and 2 furry rascals
2006 Holiday Rambler Endeavor 40' PDQ
Toad: 2015 GMC Acadia