We used external Surgeguards for 15 years on our previous Class A models and never locked them. To be fair, we were almost always in a secure RV park environment. But we do lock our tow bar - you lose one of those and your whole day is really ruined. The 2019 we just purchased has the onboard surge protection which I really like..once I learned how to decipher the EMS readout.
Hank Whitney