A while back there was a company researching hydrogen storage for fuel cell vehicles, and they came up with a liquid chemical compound called Sodium Borohydride (Na-B-H4).

This liquid chemical has a mass of 37.83 grams per mole, of which

10.66 wt-percent is hydrogen
28.58 wt-percent is boron
60.76 wt-percent is sodium

reference

The boron-11 and hydrogen could be used as fusion fuel, the rest as propellant. So, with an on-board electrolyzer a fusion-powered spacecraft could do away with large tanks and insulation for storing hydrogen (unless it also has a Bussard collector, for extreme velocities). No shielding, no radiators, no large fuel tanks or cryogenic storage. Simple liquid piping to feed fuel from tank. Such a lightweight spacecraft could have enormous payload! Or achieve enormous velocities!

I wish I knew enough to make estimates!