Fuses are there for two reasons.
1. To protect equipment
2. To protect the wiring
The fuse on your Trimetric's wiring harness is there to protect the Trimetric (equipment). Inverters, etc will have their own requirements for fusing according to what will protect that individual piece of equipment. The installation guide for the equipment will specify what kind of fuse to use.
The catastrophe fuse is there for reason 2. It is to protect the wiring. If there is a short circuit, a huge amount of current can come through the wire. This will cause it to get very hot. In the worst case scenario that will start a fire.
This video shows why you should be concerned about protecting the wiring:
Imagine that happening in your Escape.
Another point to be made from the video is that wires that are too small for the amount of current will overheat. If the temperature rises above the melting point of the insulation, the insulation will melt. When the insulation melts, the wires can touch something they shouldn't. If that happens to be something else that carries current, like another wire or anything metal that is grounded, you can then get a short circuit and fire. Good quality wiring has the temperature rating of the insulation printed on it. You can use a table to look up what size of wire, with what kind of insulation, is needed to carry the amount of current you need to carry. Search "ampacity" for more.
Catastrophe fuse location. In a DC circuit it is on the wire from the positive side of the battery or on the positive battery terminal. If connected by wire make it the first thing on the wire after the battery and use the shortest wire possible. You don't want the possibility of a short between the catastrophe fuse and the battery. That would be really bad. If the fuse is further from the battery you have the potential for the cables or something metal rubbing from road vibration and damaging the insulation thus causing a short circuit right in the battery compartment.
Standards? Well there are lots of those, and which country you are in matters. You will need to figure out what applies in your situation. Google will be helpful there. I suggest being conservative and going closer to the battery rather than further away. I'm planning on using the ISO/ABYC recommendations of ~7" or less if possible in my own trailer. That's more conservative than other standards that might apply better but I prefer to be conservative in this case. Your situation may vary.
Which fuse? You need to look at the size and type of your wires and how much current you will need to carry in that main battery cable. For most of us it is probably with a full load on a large inverter (for example, you might run a hairdryer on a 1500W inverter as your heaviest load). Add a little extra for stuff like the lights. Size your fuse (and cables!
) for that. Depending on how you have equipped your trailer and what kind of electric stuff you like to run it will be different for everyone. It needs to be small enough to keep whatever wiring you have safe and big enough that it doesn't blow when a whole bunch of stuff gets turned on in the trailer. You want it to blow when there is a need, not routinely under normal use.
There is a good article here that explains it better than I can. Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com
As far as I know, the Blue Sea fuses are very good. Their marine rated, ignition protected fuse that you have there gets some very good reviews. Ignition protected is good because of the hydrogen gas (from the battery) in the battery compartment. Enough of the people I respect use it that it will be my choice when I get my Escape. They make it in a multitude of sizes so you can pick the size you need.