You inspired me to try my luck, also being a busy DM dad. I had wanted to give shape to the idea put forth by Professor DM of Dungeon Craft of “implied space” and your post inspired me to try cardboatf. I will make some extra corners, some low walls and more archways. Here are some examples of what I have built thus far.
Budget terrain
MythBlade
#23
They are great 
love the idea of only having corners and features! No need for long walls! 
Walls can be imagined!
Again great work!
Otterlegs
#25
This is seriously cool! I’ve been wanting to get some of the dm craft terrain together for my group, I think this approach might just be the trick to finally get it done!
MythBlade
#26
Made a start on a game board to fit the “budget theme”. The edges still need doing but I’m quite happy so far 
Hans-Arsch
#27
So awesome. I just build a Kind of Garage and a Crane for my Son last Week and decidet to build some more out of Cardboard, because what would fit better the style of Runehammer Paperminis than some Cardboard. I really Love the Idea and i think i will start somewhere around the next weeks with some more Designs for a complex Battlefield like an Spaceship or maybe a Factory or something like that. I would like to have something going up the Table, with more Floors and Stairways.
Here are the Pics of my Sons Garage and some Paperminis, that explore the Terrain.
And yeah, the Lift is functional 