Awesome that it is solved!
You can clone this tank trap:
ebps\races\german\buildings\defensive_structure\tank_trap
and then edit the blueprint to:
environment\objects\defenses\metal\belgian_gate_01\belgian_gate_01
See, I tried doing something like that originally. I cloned an existing tank trap from the generic german defensive structures path and renamed it tank_trap2. I then went to change the blueprint / animator on it, and was asked to specify a path like normal. However the file path selecting window wants me to specify the path to the belgian gate files. I can find them with the archive viewer tool easy enough, but that just leads me back to the .mua file that started this whole thing.
EDIT: Perhaps if I spent more time listening to experienced modders and less time assuming I know what I'm doing, I might actually learn some stuff. For example, that I can edit the path without actually having to specify the file path through browsing and selecting, rather just typing it in as the desired animator and letting the system fill in the blanks for me - as it did.
I followed your directions, got confused, messed around some more, avoiding the .mua and other files, and happened to realize that I could manually edit the path, decided to interpret your directions literally after that and made the edit. Loaded up the game thinking: "oh boy, don't know how in the world this would work, but okay." and much to my surprise, building a tank trap, only to see a belgian gate appear. I stopped. Stared at my screen for a solid 5 or so seconds and went: "Oh. . . okay. That makes sense."
I appreciate the help and patience you put forth man. Especially the patience. I always remember playing the "All Units" mod with friends and thinking: "What if X mod had this or that from Y mod?" Like a belgian gate or Ostheer with Sturmpioneers (etc). It's a great feeling to be able to 'create' new* things like this. Thank you again.