if the car has had any sort of water leak at any point in time then you can guarantee the under felt in the carpets is damp. the issue here is that it has a rubber membrane between carpet & underfelt, so no matter what you do it will never dry out EVER
you need to strip out the carpets & under felt, & dry it all out properly
other places that cause leaks are from below the scuttle if the drainage holes arent clear, also sunroof drainage channels.
if you can leave your car garaged for a week or so, fill a bowl full of salt (the big 2kg bag) and leave the bowl sitting in the passenger footwell with all windows fully up (ie as air tight as possible) the salt will draw any moisture out of the cabin & into the salt.