Was this the tutorial? http://www.creationkit.com/Creating_a_Weapon_Mount
If so, did you add the KEYWORDS to the LinkedRef links that you made?? (spelling?)
Also, there is an issue with the tutorial (possibly with Weapon Mounts/Racks themselves, I don't know ...)
If a weapon is laying on the ground instead of being mounted on a weapon mount, just leave the room (cell) and come back.
it says at the bottom of that tutorial. Have you tried doing that?