I've not fitted a Huntsman barrel yet, but it wouldn't be critical to get as tight a fit to the standing breech as a breech loading barrel is since there's no external pressure in the form of back thrust, just the recoil of the barrel. To be accurate and consistent though, it needs to lock up good and have good latch engagement so each shot is made in the same conditions, duct tape wouldn't be a good choice to maintain consistency. Also, if there's too much barrel to frame gap, the barrel will be loose in the frame and the firing pin may not impact the primer well.
As LaOtto222 recommended, just use the barrel fitting info to get a good fit and you'll be good to go.
Tim