You could easily fab something like this:
Champ Tram Gauge (non-calibrated) - 6000
WWW.AUTOBODYTOOLMART.COM
The Champ Tram Gauge is used to make point to point measurements. A point to point measurement is the shortest distance between any two reference points. In most cases, this is accomplished by setting a dimension on the Tram Gauge and comparing it to two...
So no bending of measuring tape. Add bubble level (digital if you wish)... well you'll get the
idea.
is what i did anyways