What am I doing wrong?
Well what exactly is wrong? Model not visible? Collision not working? Exporter error?
The exporter has detail levels.
Visible Detail Level is something you see in the game. By default one Visible Detail Level is added called Detail1 and every layer is selected. (Dark box) This means you can have stuff on any Blender layer and when you export the model you can see all the stuff in-game. When you click a layer in a Visible Detail Level it automatically deselects (light box) all other layers except the one you clicked. Now if you were to select layer 1 and exported, the stuff on layer 2 is not visible in-game because it was not exported in the first place.
Collision Detail Level is not visible in-game but you can collide with it. It works exactly like the Visible Detail Level. Only stuff from the layers that are selected are exported.
In your case you have a tent model, and two collision models. It is irrelevant in which layers these models are as long as the correct layers are selected in the exporter. For example you could put the tent model in layer 3 and both of the collision models in layer one. In the exporter you would click layer 3 in the Visible Detail Level called Detail1. Then you would select Collision Detail Level from the drop drown list and click the Add: button. This adds Collision-1 detail level where you select layer 1 because your collision models are there.