What is the proper process for requesting to take a 30-day leave?

Ask your command. If they say no to 30 days upon return from deployment, and you still want 30 days, ask if there might be a more suitable time to take 30 days.

PFC (Join to see), if the unit is getting 2 weeks of leave, then that's what you get. Why are you a special case? That's what I'd ask as a commander. I'd entertain the request, but I'd want to know why. If it was justified and I was allowed to do it, I'd approve it. If it's just because you want more leave than we're authorized, then I'd deny it. Now, about the general sense of entitlement. "I'm not about that. It's either 30 days or bust," huh? I'd play rock-paper-rank with you to see how that would play out. If it's a 2 week leave policy across the unit, you'd be up a creek, so to speak. Bust then. Not even an IG would touch that. If you don't believe me, buck the system. The system will buck back.

Put in a leave request and attach justification note or write it in remarks. If it's a valid request and you are a squared away soldier, those going up the Chain may endorse favorably. I'm not sure "30 days or bust" will work out for you. The Command has to consider manning vs mission and how much leave you have on the books. If it's going to impact the unit, put you in the hole for leave, or you don't have a good reason, they may disapprove it. They can ask you to change the dates. It depends on your relationship within the unit and the Commander's policy on 30 days of leave. The regs allow you 30 days a year, but doesn't guarantee you get it all at once. 30 days in CONUS is a tad unusual but there are always exceptions if warranted. Things like getting married, helping family at home etc. I'd advise you tone down the ultimatum piece though, because it doesn't look good coming from someone of your rank and time in. You get more flies with honey than vinegar. Just my advice.