Mastercool

Buttoning up my Mastercool evaporative cooler for the season and I have encountered a problem with the 12" thick pads. Now that I've taken it all apart and cleaned it up I can not get the top of the unit back on. It's like the pads are 1/2" too tall now that they've dried out. Pad notches align with the pad support tray and I can find no obstructions anywhere. What stupid thing am I overlooking?

Probably do not have them setting into the notches on the bottom. The pads do not "grow" when they dry out. If they did anything it would be to shrink.