To reduce the condensation once you have located the leaks and to help keep the carpets and windows dry get down to your local B&Q or Focus/Homebase/Wickes. You can buy condensation traps in various sizes. They contain silica chips or granules which absorb the moisture. Once full of water they can be dried out in a domestic oven. Solves the problem of misted up windows easily and cheaply but only once you've tracked and cured the leak.
Also: check the door alignment (especially important on cars that have four doors and have been used for towing, the rear doors often lose the original setting over time). Try adusting the striker pin in the body frame (always mark the original position first with a pencil line around it). From memory all you need is a 15mm spanner to loosen the pin (one complete turn is enough). Get the door closing so that it is nice and tight with the body.
