Fat Dragon Releases 28mm Keep

Itty-Bitty,
When constructing paper models in 15-20mm, I've been cutting them up and gluing the panels to foamcore. The General Tremordon-Rederring site, located here:

zeitcom.com/majgen

. . . has excellent instructions for assembling buildings from foamcore. The 15mm buildings have turned out very well; both lightweight and very solid. My roof sections are glued to cardboard that I've saved from old pads of paper. If constructed right, the roofs of smaller buildings can be removed to place figures inside.
I have not used this method yet with the larger 25mm buildings, but I see no reason why it couldn't work. In fact, because the panels of a 25mm building are larger, the foamcore seems like a good idea to me.