There are two side supports and a cross brace in the back to hold it together. The parts are held together by some nuts and bolts on the back side.
In addition to providing the plans for my design, I will go over all the steps for you to design your own holder and cut it out, as you probably don't have the exact same model of GPS as I do.
I made this awesome piece at TechShop Pittsburgh using their laser cutters. They have an amazing variety of tools for all types of jobs and projects. Check them out at http://www.techshop.ws or stop in to your local TechShop location to take a tour. You can take classes and learn new skills and practice using powerful machines, and once you are a member you can use their facilities for your own projects.
3/4" #8 machine screws and matching nuts (4)
1/8" acrylic sheet or other suitable material
Calipers, or a good ruler
Drawing software, such as CorelDraw, AutoCAD, or Inkscape
Laser cutter, or a saw and very steady hands with a lot of patience :)
Step 1: Design
I had access to a laser cutter for the duration of the project, so I was able to test out my design and make sure it fit properly by cutting it out of cardboard after each design iteration. This is extremely helpful because it not only allows you to ensure it will fit properly, but also that you like the design. I changed several things because I found that although they looked good in my drawing, I did not like them at all after I fabricated the parts.
Using a similar system of iterative design, you can add a supporting frame that holds your GPS at a convenient angle, and maybe round off the edges to give it a sleek, polished look.
To hold it together, I added some T-slots and holes for screws so I can bolt it together easily. I got the idea for this construction method from this website: http://support.ponoko.com/entries/498833-How-to-make-interlocking-acrylic-designs
The site has a lot of good advice for making these types of connections, so please check out their guide for making strong connections in acrylic.
Make sure you leave room for the power cord! I cut some semicircles into the bottom of the supports so I can easily pass the power cable under the unit.
Step 2: Cutting the Parts
You can use your own file, or you can use my design as a starting point.
My CorelDraw file has the three main parts you need to cut out for the GPS holder. You may want to rearrange the parts so you can cut them out more efficiently on your material. If you want to cut these out by hand, I have included a PDF that you can print and use as a template. Once you have cut the three pieces out of your material, you are ready to assemble the part.
Step 3: Assembly
Now slide the side panels on and tighten the screws enough to keep it in place. The friction of the acrylic keeps it from sliding, but you could add tabs in your design to make it even more sturdy. Don't over tighten the screws or you could crack the acrylic.