I'm having a problem with inserting hoth bunkers into my map, because I always get a problem like this:

I don't know what the heck to do. Is there some collision odf I'm missing?

Terrain seems to be poking in your object. You can get terrain cutters from the asset list link and put them under your object so that terrain won't exist around the objects.

If you have small holes in the terrain around the outside of the object, you can cheaply cover them up with crate objects.