Make sure you set the fence height so that you are plunging into the top third of the joint. If you try to center you could blow out the bottom, depending on the size of the Domino.
Also do not just trust that the 22.5 setting is dead on, instead set fence and hold fence to the top of the workpiece and make sure that all of the base is contacting the bevel. I learned this the hard way joining a 14 foot long beveled frame, luckily I did a dry fit and saw the error and was able to just do a second set of mortices.
Also, the glue up is going to be a bit tricky with that long of a workpiece, not to mention clamping on a bevel. Stack the odds in your favor by pre gluing the dominoes into one side( side with tight mortices) then you only have to worry about one set when gluing. Also, only use a single tight mortice on one of your boards, with the rest in the middle position.
