Technical Need some ideas for an 8' contor gauge

Get a 4x8 sheet of luan ply and 3 1x3 board.
Cut 1 to 2 inch 8 ft strips of luan as many as you need.
Then cut some of the 1 or 2 inch strips to different lengths.
Take the 8 foot ones and lay them on the roof or body. If the body has sharp breaks
in the sides cut to the break and start again from that point. Use duck tape to hold the strips in place.
On the roof put the 1x3 and use the short strips for contact from the 1x3 to the body.
Hot glue them to the 1x3 and the long strip. Make sure you mark the location of the strip.
For the body sides do the same but support the ends of the 1x3.

Those guys that make granite tops for counters use strips of luan to get all the angles etc correct. Their strips look like a line drawing of the counter top. You will get a template something like NASCAR.

Nick