i can attest to the humidity, it was insanely hard to keep the humidity in a glass tank above 30% unless my room itself was humid.
weight can be an issue for some, i can personally lift a 40 breeder critter cage by myself, its just an awkward thing to carry. then again, ive never owned a PVC enclosure, ive built all of mine out of wood (talk about heavy)
if you wanted to, you could go out and buy thin acrylic to put over the top screen. will cost you $20-$30 at Home Depot. this might help keep in humidity, cant say for sure though, just an idea.
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