Dan,
I'd like to see your ladder mod pics if you don't mind. I have a medium Columbus Carbon on order for my Horizon (sold my ARB Simpson II) and surely will need to modify the ladder which I believe will be the same as yours. I may end up using the back entry point rather than side. By estimation the ladder would just clear or rest against the open tailgate at a perfect angle. Also, will try to rig up an MSR Parawing over the top of the tent to cover all 3 openings. Can't wait to get the tent end of Sep.
AT made me 3 taller load bars to replace the stock ones. Also, I added diamond plate to the tops of both side boxes so if I need to use the left side as a step I'm all set. Right cooking side can now handle hot pots on top of the side box (not that it couldn't before but the diamond plate sure is nice). Changed out both lid shocks on the AT from 125 lb to 100 lb which should be perfect with the new 82 lb tent once I add a down pillow top, sheets, and down comforter. Oh and I made another little goodie - removable shelf for right side of front box for two wash tubs at waist level rather than go with the sink option above the propane tank that others have done.
Thanks for posting if you get a chance...or you could send directly to me.
Wade