Another option, that is more complicated, is to separate into two electrical systems.
Separate the solar also, so you would need another charge controller....
Put one system on the big load, and the other on the rest. For example, I have one battery on the DC compressor fridge, and one battery on the coach (everything else).
I also was unsure of mixing batteries having bought the same one a year later. I like this as there is no way to deplete the battery the fridge runs on by running lights, fans, tv etc.
Also, like you, my second battery is at the opposite end of the trailer. I can put them together but this adds tongue weight and would take up prime real estate in the cabinet.
Interesting thing for me is that the everything-else battery gets run down faster than the fridge battery.
I added a breaker switch so I can electrically connect the two positives if needed. The fridge battery is connected to the alternator also, so when driving I do have option to charge both batteries together. I have never needed to yet. I have never charged off the alternator since the solar is always enough.