Carl Payne responds to some idiot (me) suggesting formaldehyde vapour to get rid of mould
That's not true at all. In fact, I'd say you have a better chance of sucking the mold and mildew out with my mom's thick furry lips.
There are LOTS of ways to do it, but leaving chemicals in an open container in your car isn't the best way. The way I use is with an ozone generator. I have one by Air Zone, model XT-2000, that I use for de-whitetrashing apartments and foreclosed properties. It will make carpet forget it's been piddled on by pets, make your garage pass a drug test and return porous materials to "neutral olfactory presence."
I have used this on my (former) '84 500SE with great (with a caveat) results. The only problem is, you coop this bad boy in a car for 10 minutes and you *WILL* get a headache if you don't allow about half an hour of it sitting out in the front yard, all doors open. Mine didn't need much, but I guarantee you the death and destruction of mold, mildew, chocolate rabbits and anything else you find patently offensive.
Chemicals mask odors. Period. You want odors, moss and mildew removed, you have to do something that not only eliminates the odor, but sterilizes the breeding ground on a molecular level. The only two things that do that are ultraviolet radiation and ozone, and only the latter leaves everything else intact (over time, dosage, etc).
You can probably get a smaller, less commercial ozone generator from a reputable store, but I wouldn't buy one that puts out less than 500 miligrams per hour (noted as 500 mg/hr or 500MGH). Those puny bastards at Brookstone and Sharper Image and whatnot put out about 12MGH and are as helpful as a Fry's salesman. If you can stand there while the thing is operating, it's not doing a good job.
And, as with any cleaning method, chemical or not, you still have to get in there and vacuum out all the "substance" that caused stink & discoloration to begin with.