I ended up mounting under rear seat, passenger side. Will save it from a lot of salt and rust winter in Utah winters. Also couldn't find a spot on frame as you mentioned.

Don't know if it is still feasible, but I mounted my air compressor for my air-lift system on my 2016 F-350 above the spare tire. It has been working fine for the past seven years. Let me know if it works for you because I have a 2023 F-350 King Ranch ordered with a 09/18 build date.

Went with an ARB Dual Compressor and mounted it in the cab behind the second row seats along the cab wall. I used the Dirt Church Industries kit. Seven years with ARB Dual Compressors, wouldn't have it any other way.

I installed mine on passenger side then made a rock guard around it. Not a lot of options but they work awesome

Put it behind the back driver seat unlatched it should fit

Move the factory harness up an inch or two and use some smaller self tapping screws through the frame, be done with it. Way over thinking this. Frame will not be compromised. Have done this over a dozen times.

Drill and move on. Not a big deal at all. Or put it in the cab somewhere.