I've added 4 12 volt receptacles.
1 in bedroom to charge phones.
2 in living area, one to feed 150 watt sine wave inverter, one to feed 12 volts for our home phone.
1 in one of the storage compartments.
3 are wired to spare fuses in the distribution panel with a pair of #14 wire each: + to fuse - to common block. The one that is used for the inverter is wired (through an inline fuse) directly to the battery with pair of #10 wire + to battery, - to common negative block in battery compartment.
Very simple to do.
Regards,
Doug