I run a 4.4 n62 with a prins lpg system. It has been excellent in every respect - I came from an e39 with an etagas system that was terrible. Tank is in the spare wheel feel and I get 73 litres of gas in it - I think it's a 90 litre tank. To get the biggest tank in you have to relocate the Positive connection on the battery (its a big block of wires). After that some routing out of the boot floor cover is needed to get it to sit flush. The rear suspension air pump the needs moving to just in front of the log tank. It's tight but can be done with no loss of boot space. To get to the battery after fitting is an hour of work but I can live with that for the cost savings. Just make sure you get a good installer and definitely go for the prins system - it costs more but the quality is excellent.