I too have a portable surge protector and have used the same one on two different 5er's for the last 6 years. If the unit was hardwired in than I would have had to buy a new one when we got our new Cedar Creek unit.
I also have a plastic locking cover that locks both the electrical cord and the surge protector together; which I use. I know this will not stop a thief, but it does help to prevent the unit from just walking away. If some one really wanted the surge protector they would probably take the electrical cord to. A 50 AMP power cords cost more than $130 on Amazon and a RV dealer this would be over $200.
Something else to worry about.
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67