Step 2 completed: I purchased an STP CAF1707 cabin air filter (2 filters in the box, both are needed, and don't ask me why STP doesn't add an "s" after "filter" on the large label on the box!) from AutoZoine for $14.99 plus tax. I saw the CAF1707 mentioned in numerous other Internet posts, along with a few posters saying it was an exact match size-wise with the GM OEM filter. I don't know if that is true or not. I do know that the width -- 5.45" -- is just barely too wide from my point of view. The length is 9.37", which is perfect, as a tiny amount of space is unused. The thickness is .86" and that's pushing things again from my point of view when it comes to getting the filters inside the opening I made.
I also ordered a Bosch C3730 cabin air filter (2 filters in the box, both are needed, and don't ask me why Bosch doesn't add an "s" after "filter" on the large label on the box! ) through Amazon.com for $39.45. It has activated charcoal attached to it. It's width is 5.24", which will be close to perfect. It's height is 9.39", which is perfect also. Try as I might, I never could find it's thickness; if it's greater than .86", I'm not going to be a happy camper. I'll make a post after I receive it.
I still remember the day I picked up my then brand new 2010 Tahoe and drove it a short distance back to Lubbock, Texas in May 2010. That damn dust and other floating crap inside the Tahoe was visible to me as the air conditioner was running. You worthless idiot GM bozos who cheaped out by removing cabin air filters after 2002, I believe, deserve to have your butts kicked. Come on down to Lubbock, Texas and I'll put on my boots to give you the kick you deserve.
Step 3 complete: A 1/8" X 1" three-foot piece of aluminum was purchased from Lowe's Home Centers. Just over one foot of that amount was cut off and used to cover the bottom of the filter housing. Some 3/8" foam weatherstripping was attached to one side of the aluminum cover. A hole was drilled in one end of aluminum cover so a screw could be used to attach it to the proper attachment point on the Tahoe (after snipping a small amount of the attachment point to make it flush with the bottom of the filter area) , with the other end of the aluminum cover pushed through a slot at the firewall end on the bottom of the filter housing. Everything is snug and sealed.