Serious questions, please:
Are you designing the box?
Do you have tools to assemble if you had a flat pack? (Lots of clamps.)
Are there limiting factors to the dimensions of the box?
If you cannot assemble the cabinet, then the flat pack is a moot topic. However, Marty Subs are designed to be about as generic as possible. They work with a wide variety of Drivers.
They could still be a possibility if you find a guy that will help you assemble them if you can't/don't do so yourself.
Otherwise, you are talking about giving a guy some dimensions and telling him to build you a box?
This is fine, too, but the level of competency on the craftsperson you look for needs to be higher. They need to have an understanding of Speakers, as well as their woodworking skills.
I'm pressing you because so far I've seen you ask about this stuff over several threads, but when asked on the specifics you tend to drop off. If you are going to hire someone, you need to know what you want, unless you plan on just giving them free reign over the project.
I still contend that finding a cabinet shop is your best option, especially if you find a cabinet guy that like Speakers.