I would imagine that several folks use wood blocks, but personally think they suck. I use 1 1/2" aluminum shims and a homemade barrel vise. I use a air powered 20 ton jack and two 1" bolts to hold my barrels in place. I have yet come across a barrel that I couldn't take off (knock on wood). I think once you go to steel instead of wood, I bet you will have better luck. Oh ya, don't forget the rosin, it does a real good job as well.
Brian