Last week, on "The Miniatures Page", someone suggested filling the card stock buildings with spray insulation foam.  I assume he meant the non-expanding type.  Anyone have any experience with this?  The idea was to prolong the life-expectancy of the model buildings, and to make them more durable.  The foam will also add weight to the models.

Another suggestion was to spray the buildings with a matte, clear coat, to prevent water damage, and to also prevent glue damage during the assembly.  It all sounds very plausible, but I'm curious about any pitfalls with these ideas.  Comments?...  Cheers!

I plan to reinforce my buildings with wooden stir sticks from now on.  They'll frame up nicely and cost next to nothing.  Spray insulation would work (low pressure stuff of course) but it seems like a hassle.
You could also mount your models on illustration board after you print them.  This is a bit tricky but once you "get it" then you got it and it should hold up nicely.  

Using the VillageWorks "inside out" trick, I've found that the double-layer of 110 Cardstock is durable enough to fit any needs I've had, and allows me to pull the roof off and show off the functional interior.  

I've never tried the mat sealer or spray foam. I have used craft sticks and wooden stirer sticks to successfully add integrity to a model. Of course they won't save it if someone sits on it like what happened to one of my models last week  :'(

I've used illustration board for flooring materials and it works really well. I've tried the double-lamination method and it worked OK. My problem with it and the illustration board was twofold: (1) It's more difficult to cut and difficult (cardstock) to impossible (illustration board) to fold; (2) Glue seperation. I had initially used glue sticks only with decent success until I tried it on both the double-laminiation cardstock and the illustration board. Both times the glue seperated leaving me with an ungainly mess! It may have been that I simply forgot to pay the glue fairy, but I've stopped using glue sticks because of this.

Hope this helps you decide.