I had to remove it AGAIN - 4th time! The carpet pad was soaked from water dripping down the inside of the firewall.

This time, I found another trick. The bottom cover comes out much easier front-end (firewall end) first. It's counter-intuitive, but there is more room to pull the drip tube clear of the firewall drain hole this way.

The wrong way: If you pull the back of the box down first, the front part pivots against the bottom of the evaporator and pushes the drip tube forward against the firewall -- not what you want. Worse, this puts a load on the drip-tube area of the box, and it's likely to break at this point. (You can't see what's going on while the lid is in place, so you can't actually see the cover wedging against the evaporator.)

To re-install the cover, put the back in place first, then swing the front of the cover upwards. You'll still have to wrestle with the whole thing to get the drip tube back up into the firewall, but it won't be nearly as difficult as trying to put the cover on front-end first.

Second tip: Remove all of the old mastic with a flat-blade screwdriver and replace with new. It's sold as windshield sealant, and it comes in 20' rolls at AutoZone. I bought 3/8" diameter sealant and stretched it until the diameter was appropriate for the A/C cover. I also put a bead of silicone around the drip tube foam where it contacts the firewall.

Third tip: The cover screws are easy to strip from too much torque. It's best to watch the box while you're turning the screw. Stop turning when the cover contacts the box (as opposed to turning until the screw "feels" tight.)