My preference is to run a trailer-wire loom from front to back and into the taillight housings, and either add bulbs or diodes with the existing. Have done it both ways, both work out well. The former can be a little more fussy and difficult if you have to drill the housing for a socket.
The diode setup works really well - isolates the coach lights from your toad lights, and easy to install.
Just run the loom from the engine bay, under the chassis, along the body framing, and in through the spare tire area. There's always a body plug you can split and run the wire through - seal with a dab of rtv.