This is a project that I've been thinking about, but pauldude000(https://www.thingiverse.com/thing:3575081) beat me to it.
UPDATE: V2 bracket has chamfered outside edges and holes for a M3 screw so you can attach flat panels to the outside of the bracket. This can work for plywood, acrylic, or fluted plastic. This may be an easier option then cutting the paneling to fit inside.
A video for part 1 is up now, https://www.youtube.com/watch?v=wDZMXot498o
Part 2 is at https://www.youtube.com/watch?v=iitrBUHP9Mg&t=342s
I remixed the corner bracket to have a slot for board material like foam board, fluted plastic / chlorplast, cardboard, or other sheet material. If you have a laser cutter you can quickly cut out your panels.
The other brackets are designed to hold the material flush with the outer edge of the PVC pipe.
Plans are for sale at https://www.teacherspayteachers.com/Product/3D-Printer-Enclosure-Plans-4538798
MATERIAL: 1/2" Schedule 40 PVC pipe. 8 corner brackets. 8 90 degree pipe clamps. 16 M3 Nuts & bolts OR 8 M8 (3/16") Nuts & bolts.
For panel material you can use cardboard, foam board, plywood, acrylic, shower curtain, or other sheet goods. You can also used chlorplast / fluted plastic from recycled political or conference signs.
Optional: You can put LED light bars or strips on the PVC to light the inside, or add a bracket for a time-lapse camera. I use the door clamps and fender washers to make a magnetic mount for a LED work light.
When you measure for this, remember that the brackets add 1 inch, and make sure the bed clears on both ends.
For the door, you can use the door clamp file, or make your own door. In mine I used PVC with right angle connectors.
For sheeting I started with 2 mil clear drop cloth, but switched out to food shrink wrap. The shrink wrap can be heated with a hair dryer to shrink it smooth. In the pictured version I used foam core board as a backdrop.