Hi
I have been towing with an LPG 4.0 jeep grand cherokee all year and am very impressed with both performance and economy.People say you get less performance on gas but i havent noticed any differance and the MPG seems to be very slightly less on gas but not much.
I have a tom tom sat nav with LPG stations as points of interest (a free download) and have towed around devon,the lake district and the north east and have never struggled to find gas.Costs vary from 42p to 49p a litre which is a huge saving,i reckon my outlay will be returned in about 12000 miles then it is pure saving.
Only thing i would say is that your conversion must come with correct LPG certificate,i have heard horror stories of botched installations.
Regards
Sean