We use 1 layer for dimensioning in SketchUp. Parallel projected views for plan and all elevations. For each view incorporate all of the dimensions you want...then in 'window-model-dimensions' choose 'select all dimensions', close the dialog box and 'group' the hi-lited dimensions. Open Outliner, name the group something logical, then after export, hide the newly formed group and move on to the next view...repeat. We usually group all of the dimension groups pertaining to 1 object after all dimensioning is complete. We used to use layers....good luck with that if you try it.