So from [date] to [date], I am going to be laid out in the sun catching a tan and reading a book.
The problem with that is people just don’t look at your signature. Whereas they are reasonably likely to notice the OOO message in the email subject header.

I used to work with someone who had a message telling people she only checked her email twice a day. You pretty much needed to call her if you needed anything outside of those times. (She worked in a remote office.) I think she had read one of those books on efficiency that recommended scheduled email time. But there were problems with this: 4. My department often had to email attachments or text to illustrate our questions/concerns. And we were on deadlines. Reading a page of text over the phone was not an efficient use of anyone’s time 5. She did outreach & was often out of the office on site visits, trainings, or travel to these places, but never ever set her OOO for these, because she was “working.” However, she was effectively not available to read emails from other staff until after hours on those days.
This is hilarious. I always read those kinds of efficiency hacks and think “wow, I wish I had the kind of job that let me set hard, weird boundaries for myself that inconvenience everyone else,” and now I learn that I apparently could have just asserted it without it being appropriate at all.