If you’re traveling to a remote, mountainous area, why not jab some fun at your lack of WiFi in your autoresponder? Plus, that makes it less likely that people will expect an immediate response or continue to email you after the first try.
Example
Hi there,
Sorry I missed you — I’m unable to get to my email right this second. Why? I’m on a backpacking trip, surviving on Spam, really good water, and trail mix. You should see the stars out here.
I’ll get back to you when I return to civilization. Or to an area with WiFi. Or to the office on May 10th. Whichever comes first.
If you need help right now, email my team at team@example.com.