I live in the country and have a 375 lb. propane tank for heat and cooking. We don't have enough outages for me to think about converting or buying a dedicated propane gneset. I've had no problems with leaving the gensets full with Stabil added, then, once a year drain and put into one of the vehicles and refill with fresh gas, stabil and a shot of sea foam.
Last time I looked, it's difficult to buy a "propane" genset in the smaller sizes, a.k.a. "portable" generators. Generac had one for a while, weird looking thing, had a bracket on the back for a 20lb. cylinder. I was mildly interested and called Generac and asked them about providing a quick disconnect to piping from a large propane tank. "Absoloutely NOT! That would void the warranty and is illegal. :-) It seems that "propane gensets" tend to be in the whole house range, 10KW+ However, it's been a while since I looked. Obviously any gas engine can be converted to propane, the only question would be how much do you value the warranty, if any, etc.