In a word, yes.
But like many things in life, it isn't a straighforward as it might first seem.
Many people are well able to fit an LPG conversion to a good standard, (e.g. if the fitter is a Motor Engineer) but they won't have the benefit of experience that makes all the difference with some of the more subtle things, such as how best to place the component parts and''Why does my engine backfire ?'' for instance. (Many models of car have 'quirks' that only show up when they are being converted. In times like those there really is no substitute for experience.) In addition, be aware that components have to be fitted in accordance with LPGA code of practice part 11, not only to assure safety (e.g minimise fire risks) but to assure your insurance company that the job has been done properly.
Don't delude yourself on the cost of your proposed conversion. Whatever a DIY kit costs there will always be parts that you'll have to buy in addition (Some examples being ; Tank mounting materials, PTFE tape and Boss white, Nuts, Bolts, Rivets, various Mounting Brackets, wire, etc.)
Also don't forget that a basic toolkit might allow you to do a good job but the professional will use a number of special (expensive!) tools to effect a conversion (e.g. Hot wire perforator for fitting dashboard switches, Pipe benders, Pipe cutters, Sheet metal cutting tools, Hole saws, Soldering equipment, Cordless and Pillar drills, Lathe, Gas analyser, Leak testing / sensing equipment etc. etc.). And a ramp makes things much easier! Doing without does not prevent a determined person from making an excellent job of the conversion, but it may reduce the likelyhood.
These are not Earth shattering facts in themselves but all or some of these things can compound amounting to a job that is less than satisfactory.
Far more significant is the question of insurance - Don't ignore the fact that you are duty bound to inform your insurer if your car is modified in any way. Conversion to LPG certainly constitutes modification in the eyes of all motor insurance companies. If you forget to inform them or simply ignore the need, this omission may come back to haunt you one day. Even the slightest of accidents can bring their assessor to inspect your vehicle and he'll spot a conversion that has not been declared. This problem may result in a refusal to have your car repaired whether the accident was your fault or not. The total loss of your vehicle's value in the case of a 'write off' is then a strong possibility.
It is possible to buy a DIY conversion kit these days, fit it and have success but your insurer is unlikely to accept your word on the quality of the job and your competence to do it. This may only be remedied by a professional Engineer's report. If that turns out to be favourable to the conversion it can still cost you a lot of money. Maybe all the money your saved by fitting it yourself or more.
Professional LPG installers have a choice of trade associations to join (e.g LPGA etc.) and should be certified as a registered and accredited installer of the equipment by the manufacturer of the equipment they fit. A good installer will be neat and tidy in his (or her) work, pay attention to detail and not be the sort of person to 'rush' the job. Such an installer should be able to issue an insurance certificate and this should be at the top of your shopping list - Check that your chosen installer can and will issue a certificate on completion of the job, get two copies and send one to your insurer.
Much better to do this and then be able to forget it, better than the worry a minor scrape could cause you when inspection time comes!
Speak with your intended LPG installer before booking your car in. Ask if it is possible to put the filler in the position of your choice, (within the installation rules) likewise with the fuel choice switch (make sure they are sensible ideas, not in the middle of the roof please! ). Look at other car conversions to get an idea of what you want, especially similar models. If the installers are not interested in your thoughts but just tell you where they want to put something then maybe you'd like to reconsider. Annoying things like a fuel choice switch mounted somewhere where you cannot see it or reach it comfortably whilst driving or an LPG filler that is hard to use can spoil a good installation. *
Expect twelve month's guarantee on parts and labour. Accept no less.
* GO LPG! will always discuss these and similar matters (e.g. tank capacity along with its siting and shape) with the customer before any holes are cut. Afterwards is too late!
(Link is currently available only when using Outlook Express browsers).