I use 12 AWG solid core without the insulating jacket (in other words
ground bus wire). I run a pair of these wires near my main line. The
wires are held in place and apart from each other with low cost wire
clamps (Digi-Key RP317-ND, 6 cents each in quantity). Now I can add
jumpers wherever necessary. The suitcase connectors are also excellent
but add cost (Digi-Key 3M155963-ND , 20 cents each in quantity). I also
highly recommend the suitcase tool if you go this route (Digi-Key
E-9Y-N, $30). With this suitcase connectors you must use a bus wire
that is 18, 16 or 14 AWG and a feeder wire that is 18, 20 or 22 AWG.
Using other gauge sizes will cause unreliability.