My DIY Finder/Guidescope underwent a major upgrade as the screw in back had issues for me to hold the DSI cam in place. Also minor focussing adjustments weren't convenient. So some hack and slash had to happen!
Have a 3.25"x2" TeleVue Extender Tube (why I have this I dunno) and it's collar fits snugly into a 50mm PVC pipe tube! In fact all 2" accessories collars fit nicely into a 50mm PVC tube!! So sawed off the main PVC tube section leaving the 50mm Collar w/lens and a small portion of the 50mm Pipe tube main section.
In the pic, you see the DIY guidescope hacked with the TV tube and a 2" to 1.25" adapter.

Here's it all together! Length remeasured to ensure focal length is retained with a better hold onto the DSI cam with the adapter. Plus I can get the parts all back as nothing is glued. With the adapter, I can still push/pull for some minor focus,..though PHD guides best with soft focused stars.

So this is the final design. Attached to scope as per previous method of the clamp rings, but added a 'L' bracket for some extra space away from scope.
Also, a food for thought,....50mm pipes will slip onto a 2" accessory collar nicely! Clamp it down, put some vinyl tape or teflon tape for a secure hold if needed. With Croys FREE lenses....have a go!! I took the remaining lens, EP, prism and constructed a small telescope for my daughter complete mounting onto a small Freebie tripod which I had stowed away!!
Good Luck!