got a 2000 ecsb that i want to put my single 10" sub in. I just want a single downfiring box that goes under the rear seat on the drivers side, one just like this

That one listed is a good price but i just dont have the money to spend but i do have the wood to build it and thats what i planned on doing but was looking under the rear seat and the bottom of the floor at the back rounds in the corners wher it goes up the trans tunnel, now im just discouraged and dont feel confident that i can build it. Bugging me, i want the box in there! anyone have plans for this box? Would make it much more simple if i could just look at plans and cut the wood..