What you are doing is great but it is only part of the process. You also need to level the crosshairs like this while the rifle is uncanted and then be able to duplicate holding the crosshairs level while shooting in the field.
I use a EXD ENGINEERING VERTICAL RETICLE INSTRUMENT at Brownells
I set the rifle in a vise and use the EXD to align the center of the bore and center of the scope by rotating the rifle until the bubble is level and lock the rifle in place in the vise. When you do that the rifle is perfectly uncanted. While it is locked down you rotate the scope while sighting on a level or vertical plumb bob as you described until the reticle is level also. Now when you lock down the rings with everything level then the reticle is perfectly level when the rifle is uncanted.
Now you need to duplicate this uncanted position in the field. There are several anti-cant devices but the one I use is the Scoplevel Anti Cant Leveling Device
which folds down when not in use
but which you can still see when looking through the scope
When you hold the bubble level you are taking all the cant out of your rifle position and holding your reticle level.