PVC Pipe kit to fit ANY size of pipe as long as it is smaller than a square Polypanel, just tweak a single number in the Fusion360 file and you'll have a new, custom sized Polypanel pipe fitting!
EDIT: As per suggestion, I have added Fusion 360 files for a Polypanel with a hole in the base so wires or other things can be fed into the pipe and also a Polypanel where the pipe can feed straight through the base.
There is an instruction sheet included in the images to help you change the pipe sizing.
There are a whole bunch more parameters to tweak and play with to get exactly the pipe fitting you need.
Included is a bunch of STL files for a few standard pipe sizes as well.