I don't think size should be a problem - if you look at 3771 Vacation house, it uses 3 of them as the floor, so 2 would suffice for the frame work houses. I'm just not sure if the bottom of the framework wall is different, and so it wouldn't fix onto the base plate.
If it was me, I'd be tempted to get a thin piece of MDF, or even heavy duty cardboard, to do the job