GPS Antenna Shelf

I'm working on a shelf for the two GPS antennas. I'm planning to put them under the engine cowl mounted to the upper engine mount. Many have put them there and don't have problems. They won't be too hard to move if I change my mind. The white one (in the picture) is for the certified Garmin GPS and the other hole is for the Dynon.

 

Here's my first test fit on the engine mount. The firewall penetration for the antenna cables is to the left of the left white antenna. Looks like it's going to work fine and was easy except that it's always hard to drill stainless.