>Do you think that you could jam a sleeping bag in there, through that small hole and then still have enough room for some clothes and food?

Yep. Round hole 8' in diameter isn't a small one
I sailed solo a small home-rebuild Russian-made catamaran(Hobie Wave dimension and perfomance-alike) on three weeklong trips, one from Manistee, Lake Michigan to Alpena, Lake Huron, one from Tampa to Everglades, Fl, and another one along Maine East Coast this year. I had two bags next to front corners of a trampoline. In one I store sleeping bag, all my clothing and tent (I use tarp-over-the-boom setup)
all my food, flashlights, stove, pot, first aid kit, drysuit when not in use, camera goes into second bag. I pack light thougth
I can right my catamaran fully loaded, I have "Bob" on top of the mast. And I have set up and used oars for windless days - Oops, I shouldn't say this

Vladimir
"The Ugly Duckling" Russian catamaran,
Unicorn old wooden A-cat