I've been thinking metal is the way to go. That way, if my printer ever has a meltdown and overheats it would have a harder time catching anything on fire. I can just put some foam board on the outside for insulation. I know that regardless, it needs to be designed in such a way that I still have full access to every angle of the printer. I don't know how many times I've been trying to insert new filament and I've ended up having to fully or partially take the extruder apart to get things going properly.
So I'm thinking the base and the sides/top need to be attached via latches so I can just unlatch from the bottom and lift the whole thing off if needed.
I know that the pvc pipe is probably a bad idea. It's cheaper, but pvc gets brittle over time, especially if it's exposed to sunlight so it might snap on you.