Universal fuse blocks are easily obtained at the local parts stores. I’ve never used a universal so I can’t say if any one is better than another.
When you’re fitting a second battery, it’s important to have a high quality isolator to allow your alternator to charge the secondary battery, but also prevent your secondary battery accessories from depleting your primary (starting) battery.
After that it’s all primary wire, split loom, firewall grommets, and cable ties.
I used this block I bought on Amazon in my 04 Disco along with a relay so it's only powered when my ignition is on. I printed a guide for it and taped it to the inside of the lid. I installed the block in the jack holder under the hood. Needless to say I upgraded my alternator to be able to power all of this plus my "regular" electrical requirements. I removed my headliner and ran all the wires inside through the firewall, up the A pillar and then down the different pillars where I needed power, like for my second and third row heated seats. There are already a lot of wires in a loom with great hangers so I just added to it. Works great. I don't have all the seat heaters installed yet so not sure if the alternator can power six at the same time. We'll see after I rebuild my motor (sigh).