JMO, direct connection is best, unless you have the desire to be able to remove it easily. Plugs and receptacles just add another possible point for corrosion and poor connections, and I can tell you that Terrovas are very picky about bad connections, especially with Ipilot, BTDT.

As mentioned, you need an inline fuse holder as close to the batteries as possible, a circuit breaker will work as well. The recommended size will be in the manual.