Make them a little long, but not so much that you have to loop the extra slack.
Longest run I ever made was a 40' subwoofer cable that did not pick up any hum, but careful placement of the wire did more for that than the shielding.
Also, XLR cables have good shielding, but the primary reason they are good for long runs is that the combined + to ground and - to ground signals cancel out any intereference. That's why they are the standard for pro gear, which is usually set up in an non-idea environment much farther away from the speakers, amps, stage, etc.
Having made both and RCA to XLR (unbalanced) adapter cables, I prefer crimp on RCA by far. 5 minutes versus 30 minutes for the XLRs. Undoing the braided sheath is a pain, then combining and soldering wires onto tiny tabs -- no thank you.
For rca, it's usually strip, pin crimp, set the body, then body crimp. Done. The hardest part is remembering to put things like heat shrink or boots on the cable BEFORE I crimp on the ends
That's happened more than once -- DOH!
Good luck.