How do you negotiate your rates with local gyms?

I’ve recently been certified through NASM and want to train my clients at a local gym, but I want to remain an independent contractor. I’ve been teaching fitness classes in the area for almost three years, so I already have a client base to draw from.

I would like to know how you negotiate rates with local gyms. Do you pay a percentage? If so, what is a fair percentage? If not, how much is too much per month?

Do the gyms allow your clients to work out without having a membership?

What other details should I be thinking about? I already carry insurance. Thanks for your help