What I mean is to go to a shop that does front end work all the time and not as an add-on or sideline.
I try to avoid dealerships and franchises like Firestone. I ask around for recommendations. I prefer locally owned shops that have been in the same spot for years. A positive local reputation is earned.

 

Lots of info and how-to on the internet for dual battery setups. Some even use GM oem parts.

Our vans have a factory option code for second battery. Sometimes called the "ambulance" option.