Help needed with Zones and Portals

I have a level which includes a dungeon and an Inn with an interior. Both models are exported as collada and converted to dts with dae2dts. Everything is fine and I can enter the dungeon and Inn. Buth due to the sizes of these objects they are eating up draw calls and so...

The first thing I tried was LOD-ding the inside, but when passing by the center of the model it switched back to the smaller LOD what am I doing wrong here >(.

So I tried setting things up with zones and portals in the world editor. No problems creating the zones, added a portal connecting 2 zones, moving this portal until it went green (difficult to do but not impossible). The problem I am experiencing now is that the engine hangs when I am entering the portal (or in close distance of the portal, I can't really tell).

Now the big thing:
Can anybody explain to me how to setup a model, add the zones and portals so that this will work. In other words: do I have to follow certain rules when creating the model (out en inside), how much space is needed between to zones I like to connect and maybe anything else I can't think about on using zones and portals.

I've searched the forums for answers and found something, but unfortunately I'm not getting any further with it.

Thanks.