Why are you doing this? Yes the factory regulator is metal and the most likely spot in the trailer to be damaged by freezing.
But if are talking about freezing during winter storage all you to do is make sure you blow the line with air before installing antifreeze. That leg of the system will never drain when draining the trailer so it has to be addressed that way.
I can't comment on the Shark Bite but will comment that those brass barrel type regulators that 90% of people are using are not pressure regulators but rather flow regulators. In fact they don' even do that in a range that would have any effect on a trailer. If you do look for a Pressure Regulator make sure you do not get a flow regulator that is sold as a Regulator. If you can blow air through it it is not a pressure regulator.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles