Printing rails-down will provide better external finish. It’s easy to do if you calibrate your printer & filament. Nowadays, you can use Orca’s Calibration Suite to do this. If you’re interested in why, you can also check out Ellis’ Print Tuning Guide. You’ll also want to calibrate support settings so they come off relatively easily with the interface so you’re not scraping it out. These are my support settings
You’ll mainly want to tweak the top/bottom z distance. You also may lower the tree support branch angle if you find them failing at large angles.
I would also recommend learning to place supports manually to save filament & time, but auto mode usually works fine. My process for this is basically just checking how the printer prints overhangs in the preview tab. If an overhang starts in mid-air, it usually needs either a support or the Counterbore holes option in Orca.
Next, you can do a calibration for XY dimensional accuracy. The Califlower (paid) or Calistar (free) work well for this.
Once you do these calibrations, all of your prints will come out better. You can just cut the frame in the slicer to only have the rails if you want a test print for it without having to print the entire frame.
OEM LPKs are recommended because they’re known to be reliable. You can have reliable 3rd party LPKs, but OEM is what is known to reliable so its recommended. Magazines are kind of the same thing. You can also print a menendez mag v3 if you want to try out a printed one :)
Aves and Riptide are great for rails. MAFCorp sells them a lot cheaper, but I’ve found them to sometimes need a little convincing to get into frames.
I usually use PSA dagger slides for mine, but it’s kind of the same thing as with the OEM LPKs. People know daggers and OEM slides are reliable so they get recommended.
I would think the material would be much too thin. Maybe you could try the fill multiline infill option? That should give it more thickness but even then maybe only for .22