Relay would be good close to the fan, in the engine compartment so it is easy to get to, IMO.
If there is a charging issue when everything is on, an upgrade to a 90 amp Alt. is possible. Just be reminded that the fuseable link and/or the wire that goes through the fire wall for the Amp meter (Which will also need to be beefed up or changed out for a volt meter) is at risk of being burnt up/out.
(Been there, done that.)