This is what I have managed to do to the card building I bought from Infinity Miniatures.
Basically I glued the whole thing together with wood glue, added packing card to the insides to add strength.
Make corner sections and seal them in with PVAcrete after I had added a hardboard base.
All in all its a lot more solid and would stand up to being played with at the club, not sure I like them though.
Hardboard base. Just incase you didn't know what one looked like ;-)
What I don't like is that they are essentially flat terrain and by the time I have fannied about adding stuff I could make something I like better.
Shame because they are nicely designed, but then they are also very cheap. Will complete all the buildings and crates as quickly as I can and get them to the club.