Has anyone ever done this ?

[hispls 5,000+ posts]

If you can make a hole to add a port in a sealed box, you can definitely build your own ported box out of scratch.
Cheapest simple way to do it, get a proper blueprint, plan your wood cuts, buy the wood at home depot, have the workers there cut it, they charge a few cents a cut after the first 3 or something. Take the wood home, glue and screw (requires an electric screwgun which you can get for 20 if you dont already have it) Then cut the circles for the sub and the port with a jigsaw. Glue or screw the port in and you are done. You'll be using round 3, 4 or 6 inch pvc pipes from home depot as well.

Its basically building a square/rectangular cube and cutting holes. A 5th grader can do it. Total comes out to be less than 50-60 with all materials, glue, screws, wood, pvc pipe etc..

OR you can modify your box but you'l lhave to break down all the dividers and only run two 8s and even that will be kind short on airspace after port displacement. To be a proper ported box, it'll be a little bit over double the size of your current sealed box.

Very much this.

I will add, it's sometimes hit or miss at Home Depot or Lowes getting good true cuts. A flush bit on the router or belt sander, or just good planning can help if they're off a bit. Finding someone who looks halfway competent to run the saw, stressing the importance of good cuts, and throwing him 10$ cash can also ensure accurate cuts.