What good are they...I'ver never used them but would this prevent oh say, crossed wires or something from damaging the unit? If so, post some links. Does the rat shack have em? Also, where would one solder this into, as in directly to the terminals or what?
What good are they...they'll keep your gear from getting fried! A short which spikes the amperage can damage your gear or cause a fire. B-A-D. The fuse will open the circuit when it's amp rating is reached, thereby protecting your gear. You should wire it to the hot (+) lead. I use a short wire from the terminal to the fuse, then connect the other lead on the fuse to the wire going to my power plug. Easy peasy.
I forget which fuses I have, but search
Mouser for PTC resettable radial fuse or something close to that. You want a fuse with an amperage rating higher than the current your gear will pull from the battery. A fuse where your gear current draw is 50-80% of the fuse's amperage rating should be sufficient. The voltage rating doesn't matter much as long as it's higher than the voltage you'll be passing through the fuse.
I'm sure there are finer details than these, but I haven't researched thoroughly. Maybe somebody with EE education/experience can provide more details.