Nice, whatever gauge/3 wire bundle of four THHN strands. Looks similar to some of the machine cording I've been using in my shop.
What is this normally covered by, a seat? Could definitely build a wall to the right of the breaker box. Would make the shore power feed super short which is nice, and not take up room somewhere else.
1987 4BTJ60 - MoonShine - 4BT/NV4500/EcoBox/NP205/D60/14B
2004 F-550 - 6.0/ZF6 - full bulletproof