I would suggest that you find a different location that will allow you to mount your pumps with the impellers facing down. Mounting the pumps flat or upside down can lead to water leaking into the electrical motor and greatly reducing it's life. This happens when the little rubber washer/seal between the motor and the impeller housing goes bad. If that washer goes bad and the pumps are mounted with the impellers down you have a better chance of water not getting in the motors.
Likewise, with the motors that low in the bilge area you stand a good chance of them getting wet. This also presents the same issue as a leaky seal.
Either way, good luck with your install and +1 for wakemakers.com.
Gone, out doing soft recreational past time with overpowered boat!