The 22 definately Requires Weight on the RearEnd when its in Mid-Motor Configuration, as it just feels too Light & you can see the Rear Bobbing around on Bumpy Tracks!
I think that the TLR Brass Weight Kit is'nt a cure, but certainly helps this + Rear Traction!
As some of you have already mentioned, it being Mounted right on the Rear & reasonably highup, it really is'nt the ideal place as it can give abit of a Pendulum effect! Specially if more Brass was added there!
If Weight is Added, it really needs to be as low as possible & as close to the Diff area as it can be! The Chassis itself would be the best place.......or the next best thing, the Pivot Blocks/Shims!
Sounds like a good idea to me!!