I built mine out of 80/20 and scrap OSB I had. Rails from Amazon.Fridge is on top and not easy… but accessible from the rear or the side. height is critical to measure for side access as well as tour fridge style door opening . Slide would be a welcome upgrade IMO. I have it strapped to the bed tied downs which eliminates front to back and lateral movement but not vertical,. I can take it out pretty easy and use the full bed. It’s fine for off road trails I go on for hunting but I would want it secured to the bed floor if it was more for wheeling or like Baja. Had the battery behind the fridge but moved it to the Molle panel. Now behind the fridge is a hatch on a hinge. I can now access the drawer contents while inside with the tailgate closed. Have used this a few times to make coffee in the am when it’s snowing out and I am not ready to really go outside . Build thread is here and you can see how I evolved it. 2025 F150 build - #20 by toomanydogs
Only thing I would change is I would have made it narrower just to the fridge width to maximize bed space. OSB is crap would not recommend , but it was free.