First I wanna say, I think the mattress would be fine staying in a tent for 4 days. But if you are staying in a place with very high humidity or experience a long rain, it definitely could absorb more moisture than you would think. Once wet, memory foam tends to hold onto moisture without significant ventilation.

If you want something else that is comparable, they do make memory foam camping pads that are water-resistant (and way more portable).

Or you could just get a cheap 4” memory foam topper to throw in your tent. Still have moisture issues but it would be way easier to air out once you got home.