I decided to attach the cupholder behind the center section of the bench seat. There is not bottom, so the bottles and cups actually rest on the back of the seat itself. It is a minimalistic design that looks great and really adds to the truck.
Step 1: Creating a Base
I then drew two lines from opposite sides to one-and-other. I further subdivided the length into quarters, such that i would be able to have 2 cups fit (see pictures). Using the largest hole saw I possessed, I cut out two circles from the MDF. I then used a soup can to trace the final size I wanted the holes to be. Using my Dremel with a sanding drum, I sanded the openings up so that the can could easily fit through the openings.
In order to attach this portion to my truck, I needed to attach a base to this. I had some left over poplar wood, so I chose this as it is a straight and strong wood. For support i cut a small triangle, put it under the center of the cupholder portion as seen below, marked the excess portion, and cut it so that it fit flush.
After I had all the pieces of the base organized, I glued them together using standard wood glue. I then clamped the three pieces together and allowed them to cure overnight.