When it comes to adding tents and having multiple pieces that make up one large tent, you would want to add the main tent and its breakdowns into inventory. Once you've added them into inventory, you will have to then add all of the smaller pieces that make up the larger unit into a relationship and give a build quantity.
For example, if you have a 20x30 tent and it takes 1-10x10 and 1-10x20, you would enter in the build quantity like this:
This would then take 1-10x10 and 1-20x10 tent out of stock when the 20x30 is being rented out.
The biggest (or largest) unit must be the Parent item (this would be the 20x30), and the smaller units (the 10x10 and 10x20) must be the child item. The build quantity The child item builds the parent item.