I use a Howe magnetic caster/camber gauge. You remove the grease cap from the spindle, then it sticks to the hub. If you have an aluminum hub, you remove the spindle nut, put a big steel washer on, then tighten the spindle nut back on. THe magnet then sticks to the washer. It is a bubble, and it is acurate and easy to use.

I called a bunch of local garages and asked if they had a set of turntables that weren't using. Scored a pair for dirt cheap. Ugly but they work.