Need Help With Modelling for Garry's Mod?

Hows it going? I have created a simple model of a metal box… I have it exported with texture and that works. The problem that I have is I cant put another prop inside the box, in Garry’s Mod.
How do I make it so that the open side of the box is actually open where I can put a soda can into or crouch into? It has like a invisible field around the prop…

I’m not too good at explaining things, so I’ll let the Valve wiki do it for me:

I do not know what I am doing wrong. I am using XSI Modtool I followed the directions in that link… I selected my model went to property -> geometry approximation and did that… but it still does not work…

If anyone can Ill send them the model file and can they create the collision model and record them making it… So I know.

Open the console, type “vcollide_wireframe 1”, then take another screenshot. That will let you see what Source is using for the collision model.