you bet. the video is fantastic since it shows you how to line the bolt and the shell carrier up so you can fit the bolt plate on it without cursing anyone's mother, that is the hardest part of the whole ordeal
as far as the mag tube go I think a really heavy torque would do it, although some blue locktite wouldn't be bad(I think it's blue, the non-permanent one). The Mag tube should stay put since there isn't much of a force acting upon it during the operation of the shotgun.
Not trying to say you should abuse your mossberg, but I have two mossbergs, one with 3-4 thousands round through with lots of slugs in there, never cleaned, and one that is my home-defense gun that has seen maybe a few hundred rounds, and they feel exactly the same after I pour some oil into the action of the field gun. They are of the identical basic synthetic model and just keep on working. You shouldn't need to clean the gun too often.
Have fun.