i've got a 03 astravan,
brilliant i would never buy a diesel again, i pay 49p litre currently, it did stop working and i had it repaired the next day was just a sensor,
ultra reliable, engines actually last longer cause the oil stays cleaner due to less carbon emmissons, i cant feel any difference driving on petrol or gas no loss of power what so ever.
price of the stuff varys a lot within 10 miles where i live cheapest is 49 and most is 65p!
i get about 130-140 ish miles to a tenner on gas and thats carrying loads of water and ladders on the roof, tank is in spare wheel well and holds approx 54 litres
my advice would be go for it you will save loads of money some people will give you negative feedback about lpg but 99 percent of the time they are telling you hear say and have never used it.
go lpg you will never drive a diesel again!