Nope, those are 3030 aluminium extrusions, it is really industrial grade enclosure that doesn't rock or vibrate. Printer "floor" is made with 8mm thick hardwood and provides good and stable support. However, if you need for any reason put paver inside... enclosure is more than enough sturdy to accomodate that. You can also make custom supports for printer Z axis to the enclosure, as enclosure is probably much more stable than printer and can provide solution to ringing. Yeah, filament area is "almost" airtight, with only a small gap where the hinges are and since there are foam filament cleaners inside filament guides, those prevent air-exchange. However, you can also add some masking tape around the filament door if you don't trust sealing rubbers and want 100% airtightness.