Four dry bags is what I am using. Two of each will be squeezed into the slot between the tramp and the hulls. The bags are tied back-to-back and their other ends are tied to the front and aft pylons, respectively. I also riveted a small eyelet to the lower side of the tramp's side rails for the middle rope to run through. This helps to avoid the bags hanging off the hull sides and dragging through the water.

Each bag has about 10 gals of volume, so I get about 40 gallons overall. Optionally, I tie another dry bag onto the tramp behind the mast. This is enough to carry a tent, cooking stuff, summer sleeping bags, air matresses, food for a few days, and clothes. Drinks and BBQ meat go through deck ports into hulls (at the aft end for better weight distribution). They'll stay cool there.

BTW, the tent will be set up on the tramp.

I like this solution because the tramp stays unclattered when sailing.

I also considered rigging a tramp net between the hulls but was advised against it. You'd increase the likelihood of pitchpoling when you put more weight towards the bows, and you will offer a large area of resistance in waves, which will slow you down (and may make you pitchpole, also).

You do have to make sure that the bags are absolutely waterproof

H77