Josh,
Undercharging is much easier to do than over charging. Once the batteries sulfate there may be much shorter life.
Since your brother is a weekend camper, I'd install 200 watts of solar and mate it to the temperature compensated Grape controller from Home Depot.
https://www.homedepot.com/p/Grape-Solar-100-Watt-Polycrystalline-Solar-Panel-for-RV-s-Boats-and-12-Volt-Systems-GS-Star-100W/204211365https://www.homedepot.com/p/Grape-Solar-COMET-12-24-Volt-40-Amp-Solar-Charge-Controller-GS-PWM-COMET-40/305498558
