Having ported and sealed sub boxes?
 

Is it a big no no? Thought about adding two more subs in my passenger side this winter. There is room to do a ported box. However the box under my dash is sealed. I like the ability to reach down and hit some of the deeper notes but don't want it to kill my SQ. So would it be the best of both worlds? Or will it sound horrible?

Well, it might not be horrible but it definitely won't be the best of both worlds. The collective bass will be soggy and indiscriminate at best, although you will certainly increase output.
A sealed woofer and bass-reflex woofer have different phase responses. A woofer and a port output in the same enclosure have different phase responses, although each emphasizes a little bit different range (the woofer has decidedly less excursion and less output through the port's resonance range). A direct radiating sub under the driver's dash has a different phase response than a sub concealed within an expansive port locker and vented via some form of grill. So the result will be phase soup, just as if each and every entity is a different distance away from each and every listener.
Good SQ bass requires good tonal construction which is very much dependent on the coaxials for the midbass contribution. It's a lot easier to manage a smooth transition through tuning with a single woofer location and single phase rotation. With multiple woofer loading types, orientations, boundaries, and locations, its impossible. Also, SQ is dependent on balance so when the subwoofers over-drive the coaxials' midbass contribution, you can kiss SQ goodbye.
Who knows what your definition of bass SQ is and what type of music you listen to. If it's a steady diet of Rap, Hip Hop and Electronic Techno, then SQ is less critical. If it's real string bass instruments played by real artists then it will be extremely disappointing.

I listen to everything under the sun but mostly alternative rock or chill music. If you were after more bass would you go with sealed under the passenger side? If cut a vent through the walk through if I put more in there.

Chase,
Keep this in mind. The port locker and adjoining appendages is an enormous cavity. That means this enclosure is very compliant. The vent will be relatively small in comparision which means it will have resistance. Think of a hollow body acoustic guitar. You will have a sub woofer/enclosure within an enclosure which is a resonant chamber....just like that guitar. It will have its own phase signature regardless of what sub you put in it. I'm not sure exactly when compounding the issue makes a difference but once it's already past phase soup, I doubt it matters much what else you add or delete.
No sub will ever sound as good or be as productive as the first and best sub in the optimum location. Everything you add will contribute in more output but the SQ will be in decline. I've given you the technical explanation and what to expect. From here, you will have to weight your priorities and make the best decision for your usage. Personally, I always like to see the primary sub and power upgraded rather than spreading the subs around the boat.

I had both in my boat for some time but went with a bigger single ported sub when I wanted more. You might want to have individual amps with phase angle adjustment on them, that is how I got them to sound pretty good. Even with multiple sealed or multiple ported configurations in different locations or orientations phasing gets to be a big challenge. There were always dead spaces in my old bass configuration where it seemed they just cancelled each other out. Of course I tuned it for the driver seat since that is where I sat and where the db mic was placed when we did the sound contests.

Get the bass mechanic CD or download it in your phone and tune the phasing and it should sound pretty good. Ultimately I feel the best approach is to try to get enough output from a single sub or multiple subs in a single location since you can't tune phasing for all frequencies.