This looks great!
3 questions for you...
1. Does the cage sit on top of the posts as well as the shelf (is it 4'x2' including where the posts are)?
2. What height posts are you using?
3. Do you think the wire shelves would pose a problem when using heat tape on the bottom of the cage?
I've been looking for a solution to put my two stacks of AP cages on casters and this might just be the ticket. From their description, it sounds like these would hold enough weight for a stack of cages.