Here is a PrintrBot Plus mount for my old Raspberry Pi camera holder for the Simple Metal. This works great on my Plus Metal (Model 1504) with heated bed, though I haven't tested it on earlier models. Please let me know if there is a problem.
There is almost zero clearance beneath the bed, so the old design didn't work. Instead, the mount now clamps around the side using two parts that screw together using the included bolt. The part can only be mounted on the right side of the printer bed. It clamps onto a rail underneath the platform, and there is a rail guide on the left that would interfere with the mount. It does not mount to the heated part of the build platform.
I recommend you print the bolt separately with 100% infill.
P.S. I switched to an alternative RPi fisheye camera months ago. You can use the following case with this mount if you have the same camera.
I recommend you print the bolt separately with 100% infill. You'll also probably need an especially long camera cable. I found the 18" one was just barely enough to stretch to a RPi mounted to the lower side of the Printrbot Plus.
Camera cables are available here: