Ladders require backing of some kind behind the fiberglass/roof material in which to screw/bolt the ladder.
Since yours did not come with a ladder, I would suspect that it does not have that backing built into the sidewall or roof and you would have to accommodate that missing material somehow. I, personally, wouldn't try to add that material as I would get it wrong. You're probably better.
I use a collapsible ladder. Recesses into itself, takes up little room and doesn't poke holes in my rig.
I've used one for many years.
2017 CC38EL Silverado 3500HD