I have the 6' collapsible step ladder sold at CW and am very happy with it. IIRC it's roughly 4.5" x 4.5" when collapsed. I now store it in a fence post under the rig, but it will also fit perfectly in the bed of the truck (6.5').
If, like you, I knew I'd be storing it in a tube/fence post when I bought it I'd have gone with the 7' as that extra foot would have come in handy a few times, especially on sites that aren't level.
Rob & Kelly, Bella & Brady (Miniature Schnauzers)
2016 Eagle 323LKTS
2016 Ram 2500 6.7L CTD
2015 White Hawk 29REKS Summit Edition (Traded)