There can be some challenges in putting all of the pieces together.  Are you planning to use the radio/motor H-bridge ?  Does your radio/motor board have extended pins on the 32-pin header ?

The RCM should have I2C headers.  You just need to connect +3.3V, GND, SDA and SCL to the SRV-NAV board.
 
The issue with using the H-bridge is that you need to get battery power to the radio/motor board, but you also need to disable / remove the onboard Recom 3.3V regulator.  I'll see if Tim can answer this, as I believe he has gone through this procedure.

The key question is which board do you need to use to drive motors. If you need the H-bridge on the SRV radio/motor board then you will need to supply power to the input of the radio/motor board as well as to the RCM. If you can drive the motors via the outputs of the RCM then all you need to do is supply power to the RCM.
 
With power to the RCM the radio, SRV-Blackfin Camera board and all else is powered except the H-bridge/motor ports on the radio/motor board.
 
Now, if you need the motor ports on the radio/motor board then then one method you can follow to safely power the system is to trim a pin on the radio motor board (the one that receives power through the RCM...if you want to follow this route let me know and I will look up which pin needs to be trimmed) so as not to get any voltage feedback into the RCM. This method supplies power to the Blackfin Camera board through the SRV radio/motor board.
 
(Note: I've heard rumors of some that have used this set up without trimming the pin, but I have not tested this so I do not know if damage will result if the pin is not trimmed. If anyone that has tried this can confirm issues then please do so.) With this method all the boards except the RCM are powered through the SRV radio/motor board so you will need to leave the Recom 3.3V regulator connected (FYI, we have never removed this as if you power through the RCM only it is bypassed).
 
 
If you only want to power the motors on the radio/motor board but leave all other power distribution to the RCM it is possible that removing the Recom 3.3V regulator from the SRV radio motor board will allow the power input to the radior/motor board header to reach the motor ports but nothing else, therby protecting the system from backfeed.
 
(I have not tested this method so check with others to verify this option before proceeding down this path.)
 
 
As far as hooking up the Nav board, if it is I2C then there are five I2C ports on the RCM (SDA, SCL, Gnd) pinout w/Gnd as pin closest to the outer edge (see RCM User Guide).
 
Hope this helps,
T. Jump