Help with crushed limestone parking pad

We recently had a new crushed limestone parking pad out in beside our garage. It was installed for the purpose of holding a new camping trailer (small 800lbs) and our trash containers. We are extremely happy with the look and size of it. The one disappointment is the material used for the fill. The fill material that they used was a ¼" crushed limestone. They said that it would pack down nicely, but it doesn't seem to that well. The trash containers are really hard to pull on it as the wheels sink down and when I back the trailer onto it, I need to put my truck into 4 wheel drive to keep the tires from sinking down into it. What are our options here? It is about 4-5" worth of limestone. Is there a way to add clay to it? I had the idea of adding concrete to it, but I doubt that would hold up to the truck driving on it. Any guidance is appreciated!