Another way to clean interiors if you do not have a wet vac, is to get 2 clean buckets of water, interior cleaner (such as autoglym) an interior sponge & finally a chamois.
'Dry' hoover the car as normal.
Spray the interior cleaner over the seat & allow to soak for a few mins, then using a damp interior sponge, start to rub the seat ensuring you frequently rinse out the sponge in 1 bucket.
Then use the chamois & wipe over the seat applying pressure to 'soak up' any moisture, finally wring out the chamois & rinse in the 2nd bucket of water.
This is also a very good way to clean head-linings, if you do the head-lining then do it first before the seats.
You can do this in pretty much any weather.