I thought about adding this to my post on zest but it came from my grandmother’s notes so I wanted to give her proper credit!
To be honest, I think that her notes on keeping citrus fruits were probably from either before or shortly after the war as I doubt that lemons and oranges were readily available to most during the war. Her notes only mention oranges and lemons but I can’t see why this wouldn’t work for grapefruits too.
I haven’t had a chance to try this to see how well and for how long it works but the gist of the tip is that you place the fruit, stem end down into 2 inches of dry sand and at least 2 inches apart. Simples!
I imagine this would be a good way of keep citrus fruit from starting to wilt whilst camping.