Hi LC, sorry I haven't responded to your post, I have had a busy weekend.

I still have not opened the link, apparently my ScetchUp is outdated and I need to go do that first. In the mean time, I thought I would comment on the drawing you posted.

I am curios about the connections of all the frame members. You mention dowels or metal rods, could you elaborate? I agree that the plexi will bow on you also. Is is a great material, and I use it a lot, but it has limitations. You may be better off going with glass, and making a shipping box for it when you move.

Have you considered the aluminum extrusion cages? That may be an alternative that suits your need for modular construction. Take a look at this project;

http://reptiliancages.yuku.com/topic/53

It is a lot more complex than what you need, but may be something you could adapt.

I'll take a look at those drawings and get back.