Small space needing bass

[Louisiana_CRX 5,000+ posts]

An amplified Bazooka Tube subwoofer may work well ... add a pair and it could sorta look like custom dual exhaust ....

 

[MrQuik]

You need a high pass crossover on the 3.5s.

I seen a few different ones do you have any suggestion

 

[fithwheel]

I seen a few different ones do you have any suggestion

250/500 hz range depending on slope. 1st order lean a little higher (6db). 4th 24db you could probably get away with going a little lower than 250. Make sure you match the ohm load of the speakers to the crossover.
4 ohm speakers you’d need a 4 ohm crossover. If not it’ll change the crossover point on a passive xover anyway.
I think you said you had 4 3.5s? If so and they are 4 ohm and you have 2 wired parallel to 2ohm to the amp and you have 4 ohm xovers you’d need one for each speaker before they are wired parallel.