I had the same thing on the Dax when I gt it on the road - so much that for a couple of years I drove without the drivers window!
I then started sealing the bulkhead.
First the bulkhead cover for the front of the engine - I ran around the outside of it with 13mm wide 2mm closed cell foam rubber. then screwed it back in place and the difference was huge!
I then lifted the carpet around the handbrake and sealed it with aluminuim tape - then reinserted the carpet
It then almost became bearable but still too hot to drive
So I then had 2 ducts from the front brake ducts plumbed in (with 2 bilge fans (4 inch) for traffic) and the difference is huge - fresh air all the time and at anything over about 15 mph no need for fans
Be aware if you drive in cold weather you may need to stuff a sponge into the duct to reduce the extra cold air as it can be a "bit too much"
See post 132 DAX Build Up