You don't really need a rack at all in a pickup, three bungee or light tie downs per bike, turn the front wheel into the corner of the bed, two straps on the handlebars, one on the back wheel pulling it to the side of the bed. I have even done this with motorcycles in the back of a pickup with no issues. The preferred method with motorcycles is to install removable wheel chocks, but I have not been able to find any small enough for bicycles.
You could mount a couple of these in the bed.
https://www.etrailer.com/Accessories...man/S1006.html