03-08-2020, 02:02 PM
I second the advice for a metalclad 3 ohm resistor. To achieve its full 25 Watt power rating it is designed to be bolted to a flat heatsink. For the summer charge application I'd expect the dissipation to be only a few watts, so you should be OK just mounting it in air. From a mechanical point of view probably still best to bolt at least one end down to something firm. The metal cases are electrically insulated from the resistor.