You can put a bar across the bed just behind back rack, to give cap a place to sit and seal at the front.
From that bar down to the bed you can install a plate, cut to fit and then seal it around the edges with ??, your choice, expanding foam?.
This could be done with wood for temp use or metal for permanent use.
You will want to make sure water can drain out from the exposed bed under the "back rack".
What you need to do first is to find a cap you like and at a length that will fit.
Measure maximum length from rear to "back rack" and from side to side.
Then call or search for a cap that has the correct width and a length that is shorter than maximum length.
You may end up a few inches short of maximum, but buying "off the shelf" cap will be cheaper than buying custom made cap.
And that length will tell you where to install the bar and plate.
And you can cut and shorten some canopies, aluminum would be easiest because the cap is the same dimensions from front to back, fiberglass caps tend to be curved so would be harder to get a good blend when putting if back together, but you really don't need the front window since back rack is there, so you could cut off the front to shorten and then cut a wooden plate to fit and then reseal and paint it
Last edited by RonD; 08-03-2015 at 10:41 AM.