I saw a post on another forum where a gentleman had taken two rubbermaid tubs and glued them together to make a larger enclosure, and then cut out an opening in the front to make a door. I believe he riveted hinges and latches to an acrylic door, it was actually pretty cool. Not something I'd want in my living room, but for an inexpensive arboreal enclosure, not bad at all.
You could probably do the same thing with other tubs (carefully cut a hole, cut out a piece of clear acrylic slightly larger than the opening, and then drill matching holes in both, and use rivets to attach the "window" to the tub). This would be secure and permanent (tight enough so that there wouldn't be a lot of air exchange, rivets done the right way can be very tight). Hand-operated pop-rivet tools are not expensive, either. Ask around at an auto-parts store.

I'm guessing the question is because there are not many LARGE plastic tubs that are clear unless you find certain models from certain manufacturers like Iris. The bigger, sturdier Rubbermaids are not clear.