My frame is 1/4" x 1/2" flat bar welded to the door, with 3/16" sliders, topped by a removable top frame screwed on.
A-This allowed me to paint all parts front and back for no rust
B- This allows me to fine tune the slides by use of shims to get the right feel. As of yet, there are no shims and the 1/16" gap feels good. But once I fire it up and it gets hot, I will be able to adjust them if needed.
C- I build for long term use, years from now, when there is a build up of grime, dirt, ash or whatever, I will be able to disassemble and clean the slider assembly. On pie vents, I use cylinder head valve springs to maintain good seal, and all hardware is stainless.