I have an old Rive 36 and bought a Preston Inception 360 as it was lighter and for the swivel seat
Hated it, so got the old Rive out, dispensed with all trays and put anything I needed to take in a carryall, and fitted a, jury-rigged, swivel seat
The Rive without trays is relatively light, totally stable, and I never pull out a tray to get something and spill the whole contents on the bank or in the drink
I think if you only use the box to sit on and to support attachments you might just avoid back problems and spillage