[RCinNC]

Both Eastern Beaver and Blue Sea make a very nice product. The Eastern Beaver is, if I'm not mistaken, a smaller package compared to a Blue Sea of the same capacity. Centech also makes a fusebox for motorcycles, though I've read reviews in the past that said that the fuses in the Centech box tended to get loose. There also electronic power distribution boxes that don't use actual fuses, but they're pretty expensive compared to the standard fuseboxes.

Eastern Beaver makes a plug and play wiring harness for their PC8 fusebox. The harness has a relay and a plug and play connector that plugs into an existing connector near the rear of the fuel tank. There's no splicing or cutting involved. The plug and play connector is for the trigger wire to the relay. The relay allows certain circuits to switch on only when the bike is on. The PC8 also includes two "always hot" circuits.

 

[OneGun]

I ran the wires for my handwarmers up along the existing wiring without removing the tank, no trouble at all.

This. Take a length of bailing wire and loop both ends, then fish it to/through the tank to the battery area. Once the bailing wire is in, attach your wiring to the end at the front and carefully pull it through.

Just did this tonight installing a 12v/USB socket. Easier than falling off a log.