Yes the air intake aka 'snorkel' is for the passenger compartment ventilation. 'Pax' = lazy way of writing 'passenger'.
I've never taken the carpets up but I do know that the black rubber U-channel trim that runs along the edge of the carpet in the footwell (by your right calf on the driver's side) will pull away from the carpet and body seam easily enough and you can then get your fingers behind the carpet easily. The seal is just a push fit, easy to get back on, so I suspect the idea would be to pull away a couple of feet of that trim if possible to give you good access to underneath the carpet. You're not taking it up, just feeling behind it for damp. Same on the passenger side.
The MGF/TF is a leaky car - or can be. It's just one thing to rule out.
I've never taken the carpets up but I do know that the black rubber U-channel trim that runs along the edge of the carpet in the footwell (by your right calf on the driver's side) will pull away from the carpet and body seam easily enough and you can then get your fingers behind the carpet easily. The seal is just a push fit, easy to get back on, so I suspect the idea would be to pull away a couple of feet of that trim if possible to give you good access to underneath the carpet. You're not taking it up, just feeling behind it for damp. Same on the passenger side.
The MGF/TF is a leaky car - or can be. It's just one thing to rule out.