How many amps is the fuse block rated for?
What size wire did you run or are you planning to run?
What are you planning to power with the block?
If you're going for something like 20A, you would come from the accessory post, first to your fuse or breaker that would be rated at 20A, then to a 20A relay, then to the fuse block. If you follow conservative wire sizing like the NEC you would use #12 wire for the whole thing.
The relay would be a single pole type like this: 1x 12V 12volt 30A 40A Auto Automotive Relay Socket 30 Amp 40 Amp Relay Wires | eBay
This relay has the advantage that it provides both a normally open and a normally closed contact. For your application you would come from your fuse or breaker to terminal 30, then from terminal 87 to the fuse block.
When power is applied by a switch to the relay coil terminals the relay will operate.
A lot of people don't do this, but don't forget to fuse the switch that will power the relay coil.
I saw where you wanted to use a breaker as well. There are a couple types of breakers you can get for this some are self resetting. I never like to use self resetting breakers since they will close back in on a short or fault. I installed a painless fuse block on my Ranger and instead of the self resetting breaker I used a separate fuse. Some people have also had issues with them failing since they're a bimetallic contact that isn't shown to be sealed from the elements very well and the internal contacts will corrode.