During our cross country trip, I found myself changing the filters on my AC units about every 10 days due to the dusty environments we were traveling. I wanted to use a home filter vice the crap already installed, so off to the drawing board.
The factory air handlers in the main living space are 6x12, a non standard size. On the fridge side of the ceiling, I made an air box to take a 12x12 filter. A quick easy mod...plus it increases the intake size, thus sucking in more air and pushing out more air... On the other side, I will either put in a 12x18 or 12x24....unsure yet though.
I started with some 1x1 and some lattice strips. I glued them together and used some finishing nails.
Then cut them to length and set overlaps so it would be a sturdy structure.
Here's a test fit.
Went inside to cut the ceiling, and taped the seams with HVAC tape.
Installed filter and cover. No I can buy a normal size filter!!