Hi Alex, I don't know to much about the trade, but hopefully have at least some useful info for you. First things first, the RAF are considering merging the aircraft engineering trades e.g weapons tech and airframes tech are merging, as are propulsion and avionics tech, so you may have to consider if you would enjoy working on airframes aswell. This would also mean 2 years of trade training rather than 1 year.
Next thing.....Weapon tech: I did some work experience with some of the w techs working on RAF Jaguars a couple of years ago and the trade seems ok. Basically your working on the "pylons" (the things that the weapons are attatched to on the jets). This includes servicing them and making sure that the mechanisms that realease the bombs/missiles etc are working. You also fit the pylons onto the aircraft aswell as the bombs etc, and put the machine gun ammo into its compartment on the aircraft. This is what I got to see of the trade, although i'm sure theres much more to it than that. Oh yeah, just remembered another thing, you also work on ejection seats, servicing etc.
Hope this helps mate.
Good luck
Adam
p.s if you wan't more info on the trade, contact llatm, i'm sure he'll be willing to help you!