Looking at your cap pictures again I want you to know your truck cap is NOT a SpaceKap!
It's a PELSUE Products Cap!
This cap was manufactured by Pelsue Products in Englewood Colorado. I knew something looked funny to me about your cap when you said SpaceKap in the title of this thread.
Great bunch of people at Pelsue. They make all sorts of safety related items for telecom and other industries. Been in business a longtime over 50 years. I am friends with the VP there who is part of this family business. Stopped by last Fall for another personal tour.
Here is a link to their main website with ALL their products and a link to their line of what they now call fiber splicing caps. That's why the cap you have is so tall, has the cab overhang and has double doors which was what they used at that time. It was probably used for fiber cable splicing.
I looked at their basic empty shell telecom trailer with off-road package for a potential trailer build.
Nice well built products all the way around. They have to be as the telecom's use their caps and trailers for a longtime and over a lot of rough terrain.
pelsue.com
Fiber Splicing Truck Insert
pelsue.com