subs get VERY warm, and you need an amp to drive it, which will also get very hot at times. therefore, a closed and small area that isnt well ventilated it very bad. you can do this though, if you modify the seat to allow good air circulation, and it doesnt affect the sound waves and air pressure too much to end up like a bandpass box (bandpass produces terrible soud quality).
I suggest you put a sub in the trunk. well ventilated, large enough to occomidate an amp + sub. amps are usually 2-3 inches thick, and 18 inches either way by 20-30 inches wither way. subs usually need at least one cubic foot of space, but the shape and design can vary to anything you want. even fiberglass a custom fit box and paint it like your trunk or car color, so it looks stock/apart of the car.
again, i suggest you look at buying from the USA, and having it shipped to england. you might save some money. look at low end Alpine for good quality, and price.
http://www.cbrstereo.com/index.asp?PageAction=VIEWPROD&ProdID=20 - $169 US, about 212 euro. i am not sure what currency you use, i think thats the euro symbol? or does england have its own currency? shipping would suck a$$, but you still might save in the end.
YOU GET WHAT YOU PAY FOR!!! if you buy a cheao deck, it will last only a while, and sound terrible. this applies to any car audio equipment.
there are groups of companies that do things to soley make money, like sony. then there are the goups of companies that have a passion for what they do. in car audio, these companies are: Alpine, Arc Audio, Resonant Engineering, Orion, Image Dynamics, Dynaudio, Focal, JL Audio, TRU Technology, Adire, and sadly only a few others. If you want stuff that lasts, that can take EXTREME AMOUNTS of abuse and power, plays amazing clarity, looks good, and the company that makes the product will provide excelent CS, then you WILL pay for it. Because it costs a lot of money to make this stuff that good will all of those features and more. If you are looking only for a few things in that list, then look at RF, JVC, Panasonic, Phoenix Gold, and basically the rest of the companies out there. You cannot and will not get the quality out of a product that is made to make corporate nerds rich, as you will with people like you and me that really have a passion for car audio, and how good we can make it sound. its a hobby to most of these companies, not really a job. they make enough money to keep up like everyone else does with any other proffession, but no more.
maybe that will help you decide what to buy.
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