It wasnt too difficult. We dug a round hole that was larger than the trampoline and then build a masonry block circular wall around the perimeter. We then added some decomposed granite to the center of the hole to give a clean look to the bottom. One thing to remember though is that if air is trapped under the tramp, it is harder to jump because of the pressure. If you see in the photos, there are two round vent pipes in the lawn area. Those are 12" vents that are piped throug hthe masonry wall. It allows for more air to escape quickly as the kids jump. The look is very finished and the safety of not having an elevated trampoline is great.
The surface to the left is a sports court. It was manufactured by Sport Court of Arizona. I would highly reccomend their services. Thanks for inquiring about our work. Jim

Is there a drainage system under the trampoline?