I'm thinking that you want to know about the perfomance and fuel efficiency of such a change.
I guess that it will really depend on the price and availability of the LP as compared to the gas/diesel. Most of the time, it seems the vehicles that have this conversion, work for the LP company:B......or are back at the shop each night, so they aren't out looking for LP while traveling around the country.
As I understand it (and I have no data to back this up:?), the LP doesn't burn as hot, so you have less energy produced, so your vehicle may not have the same performance that it had. This may be OK if you life on basically level ground, but if you are up in the mountains, it may be a factor....and if you are putting the pedal to the metal, you'll probably use more propane (more $$) per mile.
I don't know how quickly there would be a "Payback" by using LP, if there was actually one at all.
Around here, LP is not really cheaper than gas, so there is no real savings, unless this is more of a "Green" issue.
Maybe someone else has figures to answer this question? I just don't think I'd make the investment.
Happy Camping:)