Newbie with a motorhome electrical disaster!

Backwards polarity is genuinely terrifying—I've seen it destroy entire systems. The real killer is that most leisure batteries have zero protection; they'll happily dump thousands of amps through whatever's connected. @WonkyHermit, did your battery management system have any cutoff, or did it all go catastrophically wrong before anything could react? Worth investigating what failed first to prevent round two.

Mate, this is exactly why I'm paranoid about my tiny house setup. Before I connected anything, I labelled every single cable with coloured tape—red/black for 12V, then different colours for separate circuits. Took ages but saved my Renogy panels from a potential disaster. Have you considered adding fused distribution blocks? They're cheap insurance.

Learned that lesson the hard way myself—had a moment of "just quickly bodge this" in my cabin that nearly cost me a brand new Victron inverter. Now I use coloured cable ties religiously: red for positive, black for negative, and a permanent marker on every connection point. Takes five minutes, saves thousands in damaged kit.

Polarity disasters are no joke. Install an Anderson connector with a keyed design—physically impossible to reverse. I fitted one on my van conversion after a near-miss; saved me from a potentially catastrophic mistake. They're cheap insurance. Also worth considering a DC breaker between battery and load as backup protection. What battery capacity are we talking about in your setup?

Good shout from @WD40Wizard78 on the Anderson connectors. I'd also recommend getting a cheap multimeter and checking polarity before you connect anything—takes thirty seconds and could save you a fortune in damaged kit. Labelling cables like @ZoeRoss suggests is solid too. Once you've done it once properly, it becomes second nature, mate.