If your car has persistent condensation in the winter and a damp mildew smell, chances are that the foam pads in the footwells and in the floor behind the seats are saturated with water.
Yesterday I got to the source of my problem after living with a damp interior for possibly years!
A cursory check will confirm this for you: have a feel around the join of the floor carpet and rear carpet behind the seats - press down on the floor carpet. If you see, feel or hear water squelching, then you're carrying water down there.
There is no quick fix to this one: forget about gel pads, hairdryers, heaters, etc. That is only pussy-footing around the problem. The seats have to come out, various bits of trim removed, the carpet lifted. Not a major job. You will see 2 thick foam pads attached to the carpet, as highlighted in red in the picture.. The pads sit in "sumps" that do not drain anywhere - how clever is that?! Once the foam pads are exposed, that will allow you to squeeze out as much water as possible and then use whatever other means to dry out the pads.
Apparently the main cause for water ingress is blocked front and/or back drains. All 4 of my front drains were plugged with soil, probably from years of decaying leaves and other muck. I cleared out the holes using a combination of a screw-driver to loosen the muck and a vacuum cleaner to remove it. The flimsy rear drain trays need to be inspected for any holes - see other posts.
Hopefully that should do it!
