I made an earlier version for which I got a red Dramm head. I gave that to someone else. It was much shorter and had a 90 degree brass elbow on the end instead of my 45 degree. 90 is not quite as comfy for launching the water, but its nice for close and low stuff.
The head was from the old POS I had with pressure fittings and plastic. I will upgrade the head.
Whatever grade of 1/2" copper I got was the right combo of weight and length. I wanted a bit longer than the normal store ones. Off-the-shelf worked out fine.
I will give thought to handle...
I got lucky with intuition about dessicant volume.
In an ISO related article about air drying they mentioned a ratio of 600 pounds of silica gel per 1,000 cubic feet per minute at 100 degrees for 10 mimutes.
Scaled down I am very ball-park with a paint gun that needs maybe 15 cfm with much...
Decent auto paint is too expensive to go cheap on the odds and ends like tape or air filters.
Having exhausted all off-the-shelf solutions with reasonable price tags, I concluded my less-than-stellar clear coat texture was moisture related.
Onto the mission of wringing out maximum efficiency...