Jeje I know I'm not especially good explaining so I'm going to try it as best as I can. We know now the problem comes by Addon builder (newer versions) binarizing .rtm so..... Why not binarize the rtm with an older version of AB and later extract them with a PBO manager (or another)? Indeed, that was I did.

1. Put your handanimation with model.cfg (get them on A3 Character example) on the same folder (for example, WEAPON_FOLDER\data\anim).

2. Pack the pbo with the version has provided @Fennek. This will binarize correctly the .rtm

3. Open the .pbo with PBO Manager or ExtractPbo by Mikero and extract the .rtm you have done.

4. Put the .rtm extracted on the same folder as before (data\anim) and delete the model.cfg (As It's not needed now because It's a binarized rtm)

5. You will be able to pack properly with the newer versions of Addon Builder ...

Hope this will help you :)