In my experience, most permanent job employers don't like to negotiate on vacation time.
It takes more negotiation skill. I recently negotiated a 4-day work week. I took a 20% pay cut for it (totally worth it). Essentially, instead of framing it as an adversarial negotiation, I considered it a problem for us to solve together. "I want to work here, you want me to work here, but this is what I need. How can we solve this problem?" Most of the time was spent helping them overcome concerns. At one point, I said, "yeah, that's a managerial problem, but I'm confident the managers here are capable of overcoming it."