To install a liquid propane tank into the Fusion Cart or Ignite Cart, you must first remove the knockout panel in the floor of the cart.
The knockout panel may be faint if you have a dark colored cart, but will look like the picture below:
Wearing safety gloves, place your finger (or a long handled tool) through the hole the blue arrow points to. Peel the panel back, much like opening a can! If your cart doesn't have this access hole, you can simply push down at the edge to begin to peel it back and remove this piece.
Place your LP tank into the opening.