We have different boats but yes, I mounted mine on the aft port gunwale. It sits flat and has no issues with rotating or locking into place. Mount the grill and position it where you want it for cooking before marking the screw holes.
If you recently had it serviced it is typical for them to burp and the fluid level will drop. If it continues to drop you have a leak. Tap the cap a couple times. The float could be stuck and did not reset.