I don’t know if you’ve already found an answer to your questions, but I just got a pair of stacked 4x2x2 DubiaRoaches enclosures set up for my ball pythons last week. I was having trouble heating them and made a topic about it that might have a lot of helpful information in regards to heating them. I’ll post a link below in case it’s helpful. You can scroll down to the bottom, like replies 25/26 I think, for the resolution.
And in case you’re still needing answers this far after posting the question (if not, my apologies for flagging the old old topic 
):
1] They’re holding heat fantastically, and it’s under 30 degrees F outside. At least, I don’t feel like my heat fixtures are working hard. But I have 5 heated enclosures in my bedroom, and my baseboard heater is duct taped into the off position because the only place my bed fits is pushed right up against it. And my room feels fine temp-wise. So all I can tell you is that they don’t release any more heat into the room than glass aquariums do.
2 & 3] The way I plan to secure a radiant heat panel inside of my enclosures is to attach plywood over the top of the screen. I’ll get like 1/2" thick plywood, get big washers to put against the mesh from the inside, and drive a meaty screw through. Then I’ll do the same with the heat panel, just screw it into the plywood through the mesh. Cut a tiny slot for the power cord to come out through the top. And 1/2" plywood wouldn’t interfere with the 1" spacers, while holding humidity. It’s holding Ball Python humidity now with a 2’ x 3’ piece of foam over the top. If you’re worried about mold, maybe layer a tarp over the mesh but under the plywood?
4] The floor and walls feel very strong and sturdy. They take suction cups well, and are holding a good amount of weight. Additionally, after I put the first enclosure together, I climbed inside while it was on the ground and laid down to test out how spacious it is. It held my 140lbs without any issues.
5] With the locking pin, there’s not even enough room for a baby corn snake to wiggle out, no give in the doors at all. There’s no space at all for one to slide between the doors in the middle either, there’s barely enough room for the wire of the locking pin. 100% safe. But when I put my corn snake into this type of enclosure next year, I’m getting the door locks, just for peace of mind.
And they sell expansion kits for the 4x2x2’s so you can make them bigger 