https://www.cnet.com/news/fortnite-season-6-week-4-challenges/

This challenge is obviously going to heavily rely on whether you can find the Port-a structures to begin with. But when you do, recognize that you're supposed to deploy these in different matches so only your first structure counts towards the challenge.

You can find ammo boxes in nearly every structure, so it shouldn't be too hard to complete this one. You have to find them in seven different locations though, so unless you're really efficient, it might take you a few games to complete this challenge.