3D drawings are not necessary.
Do fully agree that cardboard mockups are very useful particularly if you do not know CAD. Used a lot of cardboard to make patterns for the wall coverings and cabinet panels.
100% agree with that... If I measure the vehicle and make my own scaled and measured drawings, I'm 100% confident it's right...
On complex casework or curved panels, I'll make full size mock ups with cheap OSB, hot glued together... From that it's simple to measure off those to make finished panels and/or casework... For me and my clients it's time well invested and I'll let my results speak for themselves... In the shop my primary workshop tool is a tablesaw not a CNC router... I'll be the first to admit that my kind of custom work is different than most and full size, physical patterns works best for me...
CAD for some of us = Create A Diorama...!!!...
(above) Pull out bed mock up of OSB...
(above) Finished pull-out and hinged bed platform of high density foam and carbon fiber...
(above) OSB casework mockup...
(above) Finished Baltic birch casework with zebbrawood veneer...