I just made some MDF sidepanels for my truck, and mounted a 400 watt amp right inback of the spare tire carrier. This amp is going to the subs and has a crossover. So, what is the cutoff I should put for the crossover? also, where should I ground it to? I'm going to be using 4 gauge. I know it's kinda overkill, but it's good to have incase I go to a bigger amp.