You guys aren't understanding his question.
The short answer is yes, you can.
The long answer is yes you can, but don't. If you place firearms or NFA items onto a trust, you open your family (or whomever you put on that trust) to a level of scrutinization that normally wouldn't be necessary. Remember, you have to be a certain age to be gifted or receive a firearm; certain states have laws in place for certain types of firearms and NFA items; and so on. As I understand it, everything on that trust becomes sort of a PITA for the members because of the firearms/NFA items.
Because of that, I would do a NFA specific, or firearms specific, trust. Lot of places out there specialize in these trusts and can walk you through it. I have a NFA trust for my NFA items, but no longer add anything to it. In order to do so I would have to get each person fingerprinted each time I want to add a new item. Or, remove everyone, get myself fingerprinted, add in the new item, and then file paperwork again to have everyone added back on.