Best place for 30A power

For those that have done relay connections for powering lighting with a power demand greater than the upfitters provide, did you find any spare connections handy at an existing fuse block or did you wire it direct to the battery using an inline fuse and ring terminal? I'm going to be drawing about 20 amps (assumed I would size for 30 or 25).
Thanks!

Battery or the Inverter. I used the inverter ( in the cab ) to power my sub amp, but it’s a pretty obvious 10gauge wire, that should be relatively easy to locate once you find the harness or at the fuse block.

I ran behind the grill lights and just took that straight to the battery, and used a relay for the upfitter switch.