My old trick is to use Google and search for the vehicle name and year pdf brochure, and often the manufacture will have a pdf brochure that has scaled drawings and dimensions included.
For example I searched Google for Chevy Express pdf, and found this brochure:
https://www.chevrolet.com/content/d...4_chevy_commerical_downloadable_ebrochure.pdf
Page 17 has scaled vector drawings of all the commercial Chevy vehicles for 2014 including dimensions, these are very accurate coming from the manufacture.
You can open page 17 of the brochure in Adobe Illustrator and all the drawings (templates) are true vector images and you can scale to whatever size you want for FREE. I have extracted page 17 and added it below.