Build your own box. It's easy, cost efficient, and you can do it to whatever spec you want. You can leave it sealed and use the plan you've drawn up. Just make sure the subs have the right amount of space otherwise you won't get the sound you are wanting. A sealed box will do the job just make sure you do it right. Surf the net and you can find some box designs specifically for your truck and get some ideas. Do you have a tonneau cover for the bed? You could go all out in the bed of the truck if you have it covered.