Divorced parents needs advice on how to talk to other parent.

I want to know if there's any parent out there who shares custody of your child with the other parent, I want to take my 7 year old son to the nudist resort I been all summer last year but I don't know how to bring it up to his mom. I want her to know it's safe and it's not forcing him to do it but if I can talk to him about it then I'm wondering if she will be ok with it. I can really use some help with this.