When I added electric fans to my truck, I mounted the two relays underneath the core support triangle brace that's over by the battery. I secured the relays with the triangle brace mounting bolts. The relays are well hidden under there. I installed a little fuse panel next to the relays. That painless fuse panel with the built in relay looks like a cleaner solution than what I did.
I also ran a 6 gauge wire from the alternator to the battery and connected the other main system feed wires to it with a large crimp terminal in the stock junction location over behind the driver side headlight.
THOMAS & BETTS C Tap: 6 AWG For Max Run Wire Size, 29 Die
Model 54715
https://www.grainger.com/product/3LM..._WillCall&rfe=
Harbor Freight Hydraulic Crimping Tool
https://www.harborfreight.com/hydrau...ool-64044.html