Circuit to dim 40A/12V LED chain with PWM (Arduino output)
That 4-channel board looks so cheap it would be worth customizing it for higher current. Add a beefier input connector, and maybe solder some solid copper wire to the traces that route power or ground to the output connectors. The web page you linked even suggested replacing the power connector for higher-current use.

That 170 foot antenna you're using should be good for broadcasting radio station "PWM Arduino" to the neighborhood :-)