Try something like "hardboard." Not sure what it is called in the hobby community but it is used a lot in packaging and furniture reinforcement. Basically, it is a very dense cardboard and works wonders for stabilizing models. I use it as a building material in itself a lot of the time.



This building was made exclusively of hardboard (except for the lanterns and canopies.)

SiliconSicilian, good idea, I will looking to that for another model issue with some 40k terrain. In this case though, I think it will still have the same issue as foam core. The bridge has a bunch of odd degree angles instead of 90's or 45's that are making foam core very hard to cut for.

The stock bridge will hold over a pound of weight, i recommend foam core on the bottom if you are having issues.