A relay doesn't take the place of a fuse. You should use a fuse to protect the circuit even if you control it with a relay. Just in case there was any confusion there.
Whether or not you need a relay really depends on how much power you will be drawing from the outlets, how you want to control them, and how you want to wire it up (what size wire, etc.).
If you will be connecting the outlet directly to the battery and don't need to be able to turn it on and off, just run large enough wire, protected by the appropriate size fuse and you're good to go.
If you want to be able to turn them on-off with a switch, or if you want them to turn on-off with the key, then you may want to use a relay depending on the specific situation.