Ive been looking into getting a kit fitted and the fitting center wont fit the filler in the rear unless you have a towbar fitted.
Don't go to a fitting centre, DIY. I will almost guarantee that they will do a piss poor job... Only ever seen 2 "Professionally" fitted kits that pass my inspection 
its beyond my skill level to fit and would like the certification as well.
If you decide to go for an install .. do a LOT of research on the installer ... ask for details of jobs done, and then actually contact those and discuss the work, if possible actually look at a converted car.
DO NOT EVEN CONSIDER those "do it in a day" merchants .. they cut so many corners the image becomes a circle !! (ie drilling the manifolds without removing them from the car ... think .. where does all the swarf go ?? how do they get the angles right ?? etc etc).
My conversion took 4 days by a professional company... as the man said .. a day for the engine, 1/2 a day for the electrics, 1/2 a day for the front to back plumbing, a day for the tank, and a day to set it up and test it properly.
8 years and 80,000 miles later it is still as good as it ever was ... and other than annual service (filter change) the only problem it has had was an internal tank pick-up problem (corrosion) which required a replacement tank .... and every mile I drive saves me (on average) 10 pence over petrol (15 pence/mile as against 25 pence/mile)
