ok so ive read everything and still dont quite understand. My box will be 27x25x15 (HxWxD) after all displacement it will be 4.0ft^3. Can you please tell me where i can put the port and the length, width and height it would have to be to tune to 33hz. Thanks

Is that the biggest you can build your box. If you want your sub to be in a 4cuft box , you will have to make it like 5cuft because your slotport is going to take up about 1cuft or so of air space. Google slotported box ( images ) and look at some pics to get an idea of what you need to be doing. Then go to 12volt.com and go to box/port calculator. Play with all the #s you can think of. You can use the sqaure box calculator to figure out how much air space the slotport is going to take up and add it to the box you have. Just remember to put the wood thickness in. It calculats outside measurements....

ok so i built my box and everything it sounds pretty good. Only problem now is that i couldnt really brace the box on the inside so it vibrates a lot can i just add another "layer" of 3/4 inch mdf to the outside of the box to stop the vibrating

Yes you can. You can also cut some dowl rods or 3" wife mdf and glue them top to bottom and front to back inside your box. Tie all 4 sides together.