"J"
Apologies for not replying sooner. I am in the middle of re-modeling my home that my folks 'physically' built (Mom mixed the mortar and Dad set the cinderblocks) in 1954. I stayed here during Hurricane Ike as we are the highest natural point on Galveston Bay. Spent three (3) weeks without power (ran my Honda EU3000is) and cut down trees with Stihl chainsaw every day, but no real damage.
Anyway, my use for the 44 inch box as you mentioned is for the 'light gear': pfd's, trapeze harnesses, main-sheet, small sea-anchor, collapsable oars (yes, I have paddled my ARC21

) and the other incidentals that support a successful beach campaign.
Some of our Texas City Dike sailors mount similar boxes forward on their trailers, while others simply slide them in back of their truck or SUV. I have also found this HD Poly Box to be a great 'rinse tub' for all my light gear as they do not 'bow outward' when full of water like my Rubbermaid Tuff Boxes. I can also close the 44 inch Box's sturdy lid and let the light gear soak a few days if clean up time is against me. An extended fresh water 'soak' does wonders to dilute salt-water 'in' the gear and will make things last many many more years!
Not sure about a 12-foot 'cat-box', though mine is 10 feet long .. aluminum and 'unwieldy' with the ARC21 on the trailer

My plan this winter (as a 'break' from re-modeling the house

) is to add two (2) sets of appliance rollers (AceĀ® 32 Wheel Aluminum Appliance Roller Item#: 3676352) under my cat-box, and a thin sheet of aluminum (or SS) to the trailer (covering cross-framing) so I may 'roll' the cat-box out from under the ARC21

Two (2) pieces of aluminum angle (each 8 feet long) on either side of the cat-box will act as alignment 'rails' to keep the cat-box rolling straight. Simple nylon lashing at either end will tie-down and secure the cat-box during travel .. though I am sure I will 'over-engineer' and design some kind of locking-pin system
44 inch HD poly box will ride in bed of truck.
Last, Roberts-designed "Shared Lift" concept is
"In conjunction with low drag, high lift daggerboard and rudder designs that not only improve the ARC-21's windward capabilities but also produce a balanced helm off the wind even when flying a spinnaker. Coupling the ARC-21's "Shared Lift" daggerboard design with its high-efficiency and powerful sail plan produces a combination that will sail higher and faster to windward than any other 8.5ft. wide beachcat on the market. No other beach cat is designed like this, the daggerboard is forward of the main beam and is smaller in area than the rudder, thus the basis for "Shared Lift". Sailing the ARC-21 you find a feather-light helm as you step out on the trapeze and head to windward."
Or to put it more simply, sailing the ARC21 is like 'dancing' with a full-figure woman who at the end of the night can slide comfortably into bucket seats of a Corvette (ie, trailer) and get on down the road to the next beach campaign!
Thanks
Franklin J. Viola
ARC2101