Adding a window to a fiberglass topper?

Hi all,

I picked up a commercial SnugPro canopy that has no windows at all. I would like to add a single slider for cab through access, not a full rear window.

Any suggestions? Im having a hard time finding a small square slider as opposed to the full rear window replacement.

My final goal is to carpet the interior, add lights, and have a pass through with some kind of 'window gasket' so my pup can sleep upfront.

Thanks!