Found I did not need one as my son is able to jump up on his own. Search the forums as there has been a few suggestions made here in the past year or so.
Our dealer installed a ladder as part of the "deal". Just a basic black metal ladder with plastic treads. It hooks on to the edge of the top bunk. Just clears the slide when the slide is in. It can be unhooked if needed. We leaves ours on all the time.
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2014 Ram 2500 MegaCab Turbo-Diesel
2015 Jay Flight 23MBH
Former pilot to the rich and famous. Current domestic engineer, head chef, head laundry officer, head dog walker, and pilot volunteer. Lover of tacos and soccer
I built one out of 1x4 lumber I had sitting around. Used a couple of hooks to keep it from falling backwards during use as you can't get a lot of ladder angle with our floor plan . Plus with the linoleum floor figured it would slide out too easily. It has worked great for our now 7 year old the past few seasons of camping.