Yikes! I'm surprised your built-up wing didn't just implode. You must have built it well. At sea level, the standard atmospheric pressure is 14.7 pounds per square inch.

Now some folks do hollow out portions of their foam core wing to save weight prior to sheeting and vacuum bagging, so I suppose it is possible to VB a built-up wing if you add in enough ribs and cross braces. Still, I wouldn't do it.

One major advantage with VB is that you could skip the sheeting and epoxy carbon fibre cloth directly onto the foam core. You'll have to sandwich a sheet a mylar plastic on top of the epoxy to impart a straight and smooth surface. Hi-peformance sailplane builder do this alot to get a strong, thin wing section with sharp (read efficient) trailing edges - not to mention beautiful with the shiny carbon fibre weave.