Ok, for anyone who finds this thread, the control of the rear steer was pretty simple.
In my setup, the radio is setup as follows...
Right Stick
Ch1 Ail => Front Steering
Ch2 Elv => Unused
Left Stick
Ch3 Thr => Throttle
Ch4 Rud => Rear Steering
What thru me for a loop was understanding that Sources can be used in Mixes objects the same as Input objects. To keep it easy to understand, I cleaned up the Inputs.
Deleted the ch2 Elv object
Renamed Ail to FSt
Renamed Rud to Rst
On the Mixes tab
Removed Elv mix.
Under the ch3 Thr mix, I applied a switch to act as a arming switch for throttle. I have bumped throttle with the remote hanging from my neck while carrying, not a pleasant experience.
Under the ch4 Rud mix, applied the momentary switch (SH) so that its disabled unless switch held, I also added 2 additional lines.
Name Crab / Source FSt / Weight 100 / Swtich SD middle position
Name Norm / Source FSt / Weight -100 / Swtich SD low position
note: the weight -100 inverts the signal and uses 100 % of the range
When the momentary switch is held, the left stick will control throttle and rear steer. This will rarely be used as holding the momentary switch in the on position on the right side of radio and trying to control the right stick for front steering is cumbersome. More importantly, the 3 position switch SD helps alot. When in the high position, there is no use of the rear steer. In the middle position, the rear steer will mimic the front steer and make for tighter turning radius. In the low position, the rear steer will be inverted from the front and allow for crab walking.
My wish list would be to use a 2 position switch in replacement of the momentary, and then have the mixes look that the other switch is in the high position (not used) so that you could not use the Left Stick rudder Input and the Right Stick Mix at the same time.
Looking forward to my receiver showing up next week. I will set trim's, limit range, then test.