There are several products that you can consider.
I found Optimum Opti-Coat 2.0 to be an excellent paint sealant.
2.0 is a clearcoat polymer that forms a permanent bond with the paint. Once it cures, it can only be removed with compound and buffer or wet sanding, solvents won’t work.
However, it does require some preparation; remove wax then clay bar followed by washing with general purpose to remove silicone from clay bar treatment.
I also like Simoniz 365 wax/sealant. I found that it holds up for about six months. However, I’m not sure if it is still available because Simoniz is now
marketing to car dealers a product that is very similar to Opti-Coat.
Broadway Equipment Company also has an excellent sealant that is offered in the company’s Auto Butler program. However, I’m not sure it is available unless you are a car dealer.
As for new car dealerships, you may be surprised to find many more of them are turning up the wick by adding express oil change and carwash systems to their businesses to boost their customer service index and keep their customers from straying.
As for a paint maintenance program, it may sound like a good idea but most carwash operations cannot match the perceived level of trust of a licensed new car dealership. This is especially so with legacy customers.
My advice is to find a product that you are comfortable working with and consider a price that is about 1/3 of what local dealerships charge.