I built a paintball marker holder out of PVC years ago to hold my marker. Then I got the Kobra Max 3 and realized I had enough bed space to design a paintball marker holder that I could print in just four pieces. There is a front piece, a back piece, and two copies of the side piece (three STL files). They interlock and hold the marker perfectly. The only thing you should consider doing after you print the marker is to wrap the long side pieces with some sticky tape where your tank sits to keep it from sliding. In the photos, you can see that I printed a couple of small clips that fit on the side pieces out of TPU to see if those would hold the marker in place and keep it from slipping. They only work "okay." If they worked well, I would have included those files. You're better off with some sticky tape.

Anycubic

Kobra Max

Yes

PLA

I printed this on the Anycubic Kobra 3 Max. I used PLA filament for the version shown in the photos while I worked out the tolerances. I'll likely reprint it in PETG or perhaps ABS for a stronger version that holds up the heat a little better since I live in Florida where it can get very, very hot.