The carryall box is really handy to have. I use it mostly for woods work, but it also helps a lot with fencing and other tasks around the place. It is really easy to load beyond the 1000# capacity...but so far nothing has broken.
My box is similar to ones in online videos (for example this one:
wilsonoutdoors.com - Tractor TV [scroll down to the ultimate carryall videos]).
Mine is all PT 2X lumber of varying widths (to better fit the mounting hole spacing). The side walls fold in and have channel iron slots for drop-in tailgate boards. One of the tailgate boards can be removed and dropped into seat brackets that are fastened to the sides. Most useful are the tool carrier brackets (eg chainsaw scabbard) which keep all my tools handy and secure without tying up any of the carryall space for carrying loads.
Mine has a fixed box, but I even saw an electric dumping carryall video:
YouTube - A different kind of CarryAll for 3 point hitch
I don't know anybody who has regretted getting one of these...though some may regret having bought a 500# instead of a 1000# capacity unit. The lumber (and labour) for the box are a much bigger investment than the carryall frame itself, but even with just a recycled pallet bolted on, this would be a really useful attachment.
BOB