There was a period of time where companies producing short DP's used the LP generators because of space issues. They were never a good choice. They used a lot of fuel, which was limited by the size of the propane tank, and they were louder than the diesels. 
If you see a coach you really love, the LP would be a no deal, unless you INTEND to rarely use it, otherwise you'll be dissatisfied. For those who say they are a good choice, have them show you one manufacturer who has used one in a DP in the last five years. I think the only place you might see one still, is in a slide in truck camper. Even than I would opt for a portable Honda.