Originally progress was not tracking. The devs fixed it and tracks fine now. Below is my solution from previous versions of the same Challenge.
Boot up a new Lifeline and get to the base. Once it's secure just put all your current items in to the locker and take out the Grenade Launcher plus its ammo and the five grenades.
You'll have this fenced area to the left of your base which you can safely shoot and throw your launcher ammo/grenades at.
Left of the fenced area will be some dumpsters you can climb up and do the same.
Just alternate back and fourth between these two spots and you should be done in minutes.
Credit for this solution goes to Pinski.