Heres a short tutorial on how i made an overflow for my new 4.9g pico.
A peice of ABS or acrylic the size you need.(in this build 8" x 8.5")
Router with 1/4" straight bit and 45 degree V groove bit
Mark your dimensions. (in this build 2-1/4" in from each end a line was made)
Set your router up with the V groove bit and run your groove along these lines:
Mark your teeth. Since the bit is 1/4" you will want 1/4" gaps between each tooth.
This doesnt always work with your dimensions so you will have to play with it.
Set your router up with the 1/4" straight bit. Its best to have the bit quite exposed its
less likely to chip the plastic.
Using a straight edge and a board with some clamps as a backstop for depth you can
get the teeth very uniform in depth.
Get your heat gun out. This is were the V grooves come in. Heat slowly on both
sides of the V groove until it is soft enough to fold over. The groove with give
you a straight even bend. Use a straight edge to get a 90 degree angle.
Repeat Step 4 on the other V groove.
Paint with Krylon Fusion and Enjoy the finished product!!