Did I see another thread where you ID'd the battery as 12V in hindsight
Sounds like you are on top of the wire gauge vs current issues and will be fine in this endeavor.
While not exactly the same, if your interested, I re-wired my trailer due to poor design by Starcraft. They put the converter at the tail with the batteries at the front - 20+ feet over a 8 gauge wire. Those poor factory batteries probably never got a full charge. I re-wired as outlined in my blog below.
Sounds to me like you are reading the right info to make this work well....