First of all working in a van for a long haul will probably be painful for your back. No standing desk no office chair and desk set up will not be comfortable to code for more then a few hours.
Most of time working remote you need power and wifi. There is an expectation that you will be online during similar hours as your co-workers as peers. Maybe not exactly but similarly. So you gotta have a pocket wifi if doing this.
Working in a van most days alone can be isolating. Trust me you will feel it. Even when you go to an office and don't speak much to people it still helps with social aspect. Being online and talking to co workers does too. If you have a pocket WiFi and are not totally off grid able to engage with famile or friends and colleagues online then it will be helpful.
With climate change worsening sometimes it's hot really hot. It will be difficult to be outside for long stretches of time in a wide variety of places due to worsening climate change. When you are in the office you will not notice how bad it's getting less. Reading the news daily and seeing all the issues connecting to climate changes helps but working outside you really feel it directly. Historically a town might have had temperatures of 23 C now it's 28 C to 30 C on the bad days. However during working at an office you are usually in an AC building from 9 to 18 missing the hottest parts of day. When you work remotely to you will know how bad things are and it will trouble you more if you try to work in a van connected to nature. It's gonna be hot.
Working remote is great but there are some drawbacks like everything in life. Those you need to be mindful of before onsetting on that path.