Should I add a crossover or equalizer to my stereo

When I installed my stereo in my boat last year I didn’t thinking of adding a crossover or equalizer in my boat because my amps had built in crossovers. I run all PPI amps so I figured it would be ok. But now I’m wondering if I’m missing out on the benefits of a crossover or equalizer. So what do you think, should I get one and if so does anyone have any recommendations?

I have three amps. One for the interior boat speakers, one for the tower speakers and one for the sub.

You shouldn't need a crossover. You already have an amp and crossover dedicated to each set of speakers. Unless you wanted to use an external crossover instead of the built-in crossovers. I use an external mounted under the dash so I can adjust the volume levels of the tower speakers and subs independently on the fly.