My limited experience without a cover, parked in some light rain:

No water inside in cockpit seat or panel area. Maybe just a tad bit from the butt rib area, dribbled down the inside of the doors. I do have my boot cowl to windshield joint well sealed with silicone.

The only appreciable water inside was in the baggage area, coming from the slots in the turtle deck.

Didn't see it but assume there was also water entry in the tail area from the slots in the stabilizer access panels. Do have drain hole in the back bottom fabric.