So, couple of things. Not everyone is onboard with fusing the negative terminals, but I do for the following reason.
If the stock ground strap from the battery to the body were to come disconnected or get pinched/cut somehow, the amp chassis and ground wire becomes the new ground path back to the battery. First time you try to start the car the amp goes up in smoke, and possibly the wiring as well. The fuse might not save your amp, but it would prevent the wiring from becoming overloaded and starting a fire. Is it rare, maybe but if you are the one...
Optional, not everon agrees that you should. As for the rest, here is what I would do. First, when the combined amperage is 300 or less, I use quick acting push button reset breakers like these. They are much fastre acting than fuses.:
Amazon product ASIN B09GXXK11J
Additionally, because I’m running all my grounds back to the battery terminal in the front, I run double the amount for ground. If you are going to chassis ground, no need to do this. You could remove the fuse that you have under the hood and just insert one these breakers in its place and use your existing fuse, in-line prior to the rear battery (as close as is possible) to the rear battery. Then I use a single to double terminal mount on the battery like this one (relative to your battery, post or screw) such as these – use one of the 1/0 receptacles as for the cable you are connecting from the front battery and the remaining receptacle for the next runs run to the 1/0 to dual 4awg block for your amps:
https://www.amazon.com/Amplifiers-Car-Audio-Video-Electronics/b/?ie=UTF8&node=898116&ref_=sv_e_car_7
Or these (the ones I recently used):
Amazon product ASIN B001H4Y5OA
Now you have the batteries connected and fused, ready to go. From the 2nd battery, run a short 1/0, say 12” or whatever works power lead and if you are grounding this in the back too, 1/0 to your ground choice within 18” of the 2nd battery.
Then use one of these from for your power lead to power your amps:
Amazon product ASIN B089CGX68J
Then to a CAP (if you’re using one), then to your amp(s). You can use a grounding block or separate ground leads, 4 gauge or larger to the grounding points you wish to use. I provided this to show the direction and placement of the fusing, you can use ring terminals or other connecting blocks, whatever, as long as the placement mimics this path, you’re good to go.