Ian Dickson firstname.lastname@example.org sent me an email with his solution to spraying large quantities of strips, girders and plates.
The frames are made from pine, the supports are made from nails as well as plastic cutouts shaped to support the parts.
In the last picture you can see his primer coat sprayed on the first batch. Good luck, he is restoring an entire set ten to Red / Green!
Ian also mentions the following advice. "A friend who restores cars, told me to flatten down the primer coat(s) with wet-and-dry, soap and water using soft rubbing-down action. I did this and the finish after final color coat is just fantastic."