i cant think of a reason why plywood wouldn't be good for tortoises. In fact the sealant might release more VOCs than the plywood glue.
i've heard of people using something similar to pond liners to keep the wood dry
As long as the wood is inside, you don't need sealant. Even outdoors, unless it's super cheap *** particle board, it should stay in decent condition.
I've been using the same pine 1"x12"s for almost 4 years outside.
If pine mulch is bad for them as a substrate why isn't pine plywood bad for them? People with environmental sensitivity are building houses using 'green' plywood that doesn't contain formaldehyde or toxic glues. Shouldn't we be concerned about the effect the chemicals that outgas from lumber will have on our reptiles?
the substrate is dusty and in small amounts, where as plywood is fine to build for an enclosure since its not in small amounts theres hardly any dust or fumes coming off it.