Putting a shell on will help a lot, but as Martin said, the bed isn't sealed and the newer Tacomas are much worse than the old ones in that regard. I went through and taped my seams, pulled the side cubbies and ran a bead of silicon around them, got up underneath and put rubber strips over the openings that the tabs for the rear cubbies have and put one of those rubber tailgate seals on mine. It's much better but it still gets some dust in it and it hasn't even been in the desert yet. My recommendation? Trash bags and/or waterproof bags. Pelican style case if they're within your budget.