Any circuit should be protected, especially if it is run through a metallic object such as a bulkhead. If any part of the wiring touches ground, without a fuse or breaker, it can start a fire, damage the wiring and anything around the problem.

An inline fuse can be added in the battery box, just where the new wire is attached to the B+ terminal. You can also purchase an automotive fuse base and fuse replacement with an auto reset breaker. Once that is installed, you won't have to worry about blowing fuses.

It all depends on how you plan to use the circuit. If you are installing a single light or plan on later adding appliances, the amperage you will need will vary. Generally, if you install 12 awg wiring and a 20 amp breaker, you will have a circuit heavy enough to handle most circumstances. A lighting circuit only, can manage with a 16 awg wiring and 10 amp fuse. The difference in cost between the two is minimal and it's always better to go with the heavier duty. The installation labour is the same.

Auto parts store do sell these products. Make sure the wiring is multi stranded and not a solid core. Also take in a supply of rubber coated clamps (adel type) for the run and grommets wherever you plan to penetrate the bulkhead.