Ace,
FWIW: I bought a new Columbus small x-long a year ago from Mike & Gary. Ordered mine sans mattress...been down that road before

. Its just me up there...so a little less complicated to arrive at a relatively compact but super comfie mattress solution: Exped MegaMat 10. Along with a down pillow and Western Mountaineering Sequoia if I'm careful packing the pillow and bag towards the rear, as Colin mentions above, with the sleeping bag fully opened to reduce its height...then I can just get the top clam closed properly.
The ease or lack of closing/latching, for mine, is directly related to the volume of goods within the Columbus. If I remove the pillow or sleeping bag or deflate the MegaMat then it closes and latches quite easily.
My only complaint about it: The bug screens velcro on to the sidewalls of the side-doors. Obviously whomever thought this was a good idea never spent more than 30-seconds in a tent. Hope they changed it for your new Columbus.
Dan