pull out drawer question

I have heard that many folks make the galley outside the trailer rather then build it inside the trailer back area.
https://www.youtube.com/watch?v=Xy72BfqSX4I
This video shows how to install a slider
I at this point am building the galley as I go inside the trailer.
as I watch the video, reality struck how do you install a slider against a wall?
Answer you do not you build that part outside the trailer and insert it inside the trailer with the drawer and slider already attached.
I like to be 3 to 5 steps ahead before I get there so it is thought out first. I am designing as I go. This can be exhausting and frustrating at times.
The sliders I will install will be for pull out cooler. there will be another pull out that will have pull outs top and bottom. And there I can attach the pull out units to base and cabinet outside the trailer then, slide the entire unit in the slot and attach the top and bottom outside wall to the cabinet next to it by drill screws in through the cabinet wall into the top and bottom outside walls of the vertical standing slide unit.
something like this
this is not exactly it but close.
I have seen hundreds of galleys with pull out coolers but never asked how they got the pull out unit on the wall side in.
Ron
https://www.youtube.com/watch?v=Xy72BfqSX4I
This video shows how to install a slider
I at this point am building the galley as I go inside the trailer.
as I watch the video, reality struck how do you install a slider against a wall?

I like to be 3 to 5 steps ahead before I get there so it is thought out first. I am designing as I go. This can be exhausting and frustrating at times.
The sliders I will install will be for pull out cooler. there will be another pull out that will have pull outs top and bottom. And there I can attach the pull out units to base and cabinet outside the trailer then, slide the entire unit in the slot and attach the top and bottom outside wall to the cabinet next to it by drill screws in through the cabinet wall into the top and bottom outside walls of the vertical standing slide unit.
something like this

this is not exactly it but close.
I have seen hundreds of galleys with pull out coolers but never asked how they got the pull out unit on the wall side in.
Ron