For those who may search for this info. in the future ....
Toilet height without lock-down base: 17.5"
Toilet height with lock-down base: 17-7/8"
Width of "Curve": 14.5"
Depth of "Curve": 17"
The FWC rear shelf will have to be either removed with use of "Lock-down" base ... or slightly modified in height for use without Thetford "lock-down" base.