IT CAN BE DONE!
The space behind the seats of a reg. cab ford ranger (91-95 model) is roughly 13" in height, 36" in width, 7" thick at the bottom and 2.5" thick at the top. The biggest working enclosure i could build with the stock seats in place (all the way back) was one with almost .5 cubic foot per chamber. The only problem you'll run into is mounting depth. You cannot put the speaker holes in the middle of the box as you usually would. You have to mount them at the bottom of the box, and more than likely build the box to have the face the speaker mounts to stick out about an inch and a half farther than the rest of the box, to make sure the speaker has enough clearance to fit. There are some online companies that sell custom fit boxes for reg. cab rangers, but they're not easy to find, and expensive to ship. Just try to find some pictures so you'll have something to look at while building yours. Before I bought my ranger, I installed a pair of 10" pioneer tsw-253c's in a 92 ranger reg. cab, so I know it can be done. I swapped the stock seats of my 95 ranger for a pair of buckets out of a ford escort, and it actually gave me enough room to install a pair of 12's, but with the stock seats in place, you can forget about that. That's why I call it the Lone Ranger ..... I've never seen another one with 12's //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif