I just cut/pasted this from another thread and summarised. It is more appropriate for your plans of mounting a small/medium sized CRT, so I cut/pasted rather than just linking.
To mount the CRT all you need are four pieces of decent offcuts from a strong wood like 3/4" plywood (MDF may not be strong enough). The four wood offcuts only need to be maybe up to 3-4 inches wide and a bit longer than the sides of your monitor.
The first two wood pieces are just for blocking. They just need one straight edge and are screwed flat into the side of the monitor bay at the angle you want the screen to be.
The other two wood pieces will bracket the CRT, and the weight will rest on top of the blocking pieces. To let the brackets snuggle up to the CRT corner pegs, cut part of the wood straight at roughly 45 degrees (like shown below). This will give you some wiggle-room, as the angle will always come to the corner pegs optimally. You can then just slide the two pieces to the tube so that they always fit perfectly.
If you cut the 45 degree angle part long enough, say up to two inches or so, it is easy to swap out the tube for another of similar size. You just slide the wood brackets up and down to find the right spots for the CRT pegs and drill a new hole
The CRT in pics above is resting very happily there, even though it is not bolted down!
Use T-nuts like these to secure the tube:
You can use this same mounting method with commercial metal arcade monitor frames because they will have mounting flanges on the outer edge.
If you need to attach the degaussing coil around the outside of the tube, I suggest cable ties. You can screw the TV chassis to an offcut piece of wood, and then either screw that to the inside wall of the cab, or make a wooden shelf below the CRT neck.
We should sticky this as it comes up every few days.