Polar 24 Pack Soft Cooler works exceptionally well for me. The insulation provides padding and the shoulder strap that comes with the bag works okay for me too. I simply put my rig in the bag during surface intervals with a towel over the top of the camera rather than using the bag as a fresh water rinse tank.
After getting a dome port dinged pretty good last year in a boat rinse tank, I stopped using the boat tanks. I also have watched too many non-photographers use the boat tanks as mask rinse tanks frequently despite instructions from the boat crew not to do that.
I do use the cooler as a fresh water rinse/soak tank when I return to my hotel room... just set it in the tub or shower and fill it up (just make sure not to cover the tub/shower drain).