Camp equipment is 2-wide x 4-high . Meaning you MUST have 2 slots open in one of the 4-high rows underground in order to place the item. It isn't necessary to have the 3-high rows cleared first, just scroll down past the 3-high rows until you get to the first 4-high row You cannot buy the item unless you can place it (but you can always put it in inventory if it replaced another item.)
The Event ends on Tuesday, but you'll have a week to buy the Equipment.
CONVERTING DIVINE ICE TO COINS:
If you're continuing to collect the Divine Ice from the Repeatable mines, make certain you convert it to Coins BEFORE the Event ends. While you'll have a week to buy the Shop items, you won't be able to get more coins after the Tuesday update.
Hope this helps. Happy digging🙂