With Trioxane, if the foil gets broken, oxidation will degrade the fuel, not optimal.

Hexamine will also oxidize over time if not sealed, and it is not waterproof, the copressed bar/lozenge breaks up...

I find that I choose Pitchwood or Fatwood for it's solid and water-resistant form. Alternately, cotton balls soaked in white petrolatum(vaseline) are a good tinder, though if you get too much white petrolatum in there, you will have to get the excess out before it will light easily, but then again, the excess makes for better water resistance.