Memphis Subwoofer Box

I have a memphis mono amp rated at 250 watts @ 4 ohms and 500 watts @ 2 ohms.
I have a full size chevrolet truck extended cab.
my speaker set up is like this. dual 10" subwoofer box under the back seat firing down.
2 10" memphis subs, wired at 4 ohms. meaning my amp its throwing 250 watts making it
125 watts per sub. the subs are rated at 200 watts each. so I assume this is not the optimal
rms that the subs are taking right? I am 75 watts short of the 200,
I want more bass out of my 500 amp. So I would like to now what would be better if I want my bass
to be heard not only inside my truck but also out side. 2 15" memphis speakers running 250 watts each.
or 1 15 " kicker running 500 watts and of course box options are with a ported box seating on my back seat
please give me suggestions on how to maximize the bass from my memphis 500 amp. because my original set up
honestly gives nothing of bass. I plan on matching the rms from the amp and the subs next time.
thanks. ppl