Six Jobs, Not One

People talk about "the battery" like it's the whole system. It isn't. A camper electrical system has six distinct jobs, and every component in the bay exists to do exactly one of them. Once you sort the parts that way, the wiring diagram stops looking like spaghetti and starts looking obvious.

Everything That Goes in the Box

Before a single wire gets crimped, every component gets staged in the compartment — bus bars, fuse block, breakers, AC distribution box, outlet — and shuffled around until the layout makes sense. Positive side on one half, negative on the other, AC kept physically separate from DC, and nothing mounted where you'd have to remove one part to service another. Spending an afternoon on this is what keeps the finished bay from becoming a nest you're afraid to open.

Two Ways to Charge the Battery

Sun and shore. Solar covers you at a no-hookup campground; the shore inlet covers you in the driveway the week before a trip and at the occasional powered site. They charge the same bank through two completely separate paths, which means a failure in one doesn't strand you.

A third path worth knowing about: a DC-DC charger that pulls from the tow vehicle's alternator while you drive. We left it off this build because the two sources above already cover our use, but if you tow long distances to dark, tree-covered sites, it's the upgrade that pays for itself. Never wire the alternator straight to a lithium bank — a DC-DC charger between them is what keeps both alive.

On the Roof

A teardrop roof is a compound curve, which generally rules out bonding the rigid aluminum-framed panels most RV solar advice assumes straight to the skin. Plenty of teardrops still run rigid panels — mounted to a roof rack or crossbars that hold them clear of the curve, which keeps the air gap and the better yield that comes with it, at the cost of the rack itself, some height, and some wind noise. Going flexible trades the other way: the panel bends to the profile and bonds flat — no rails, no standoffs, no four holes drilled through a roof you just spent a week sealing. That tradeoff is real too, though. Flexible panels run hotter because there's no air gap underneath, and hot cells make less power. You give up some yield to keep the roof clean and watertight, and on this build that's the trade we took.

A panel's positive and negative leads both drop through one double cable seal — one seal per panel — and run down inside the wall to the controller. We use Scanstrut horizontal seals rather than the tall dome-style entry glands sold with most solar kits: they sit much lower to the roof, which matters on a surface that already catches wind at 70 mph, and they hold up better over years of sun and weather. We run two panels, one ahead of the fan and one behind it, so that's two seals and two penetrations in the roof besides the fan itself. The alternative is combining the leads up top and going through once, which trades a hole for a joint sitting out in the weather — we'd rather have the second seal. The fan itself is the other 12V citizen up there — a powered roof vent does more for sleeping comfort in East Tennessee humidity than any amount of battery capacity will.

Protection: The Part Nobody Photographs

Here's the rule that matters most and gets ignored most: fuses protect wire, not devices. You size the fuse to the smallest conductor it defends, not to the appliance on the end of it. A 40A fuse on 16 AWG wire is not a safety device — it's a heating element with a delay. Get this backwards in a plywood box you sleep in and the consequences aren't theoretical.

What It Actually Runs

Rough daily draw on a normal three-season weekend, which is the number that decides how big a bank you need. A 12V compressor fridge duty-cycles rather than running constantly, so it lands around 25–35 Ah over 24 hours depending on ambient temperature and how often the lid opens. The roof fan on a medium setting overnight is another 10–15 Ah. Interior LEDs are almost free — a few amp-hours an evening. Phones, headlamps, and a camera battery add maybe 5–10 Ah.

Call it 50–70 Ah a day with the fridge running. On a 100Ah lithium bank — where nearly all of that capacity is genuinely usable, unlike lead-acid — that's a comfortable night and a half with no charging at all. Add solar and, on an open site in good sun, you're roughly breaking even day to day. Park under Smoky Mountain canopy in October and you're not; that's exactly when the shore charger and a full bank before you leave the driveway stop being redundancy and start being the plan.

Sizing It for Your Own Build

None of the numbers above transfer directly to your build, because your loads aren't ours. Rather than copy a parts list, work out your own daily amp-hours first, then size the bank, then the charging, then the wire, then the fuses — in that order. We built a tool that walks the whole chain and spits out a wiring diagram, a parts list, and fuse sizing for your specific setup.

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The exact classes of component in our bay. Sizes should follow your own load math — see the builder above before you buy.

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