My trailer sits on 24x24 patio stones. I had 12x12 side by side about 6 feet long. Last year went to the 24x24 but didn't take the time to make sure the ground under them was level. I will be replacing them before winter this year, because they are all cracked. I have some screenings that will level out the area before the new ones go down.
The 12 x 12 fit the tires but it was a pain to get the angle just right every time I backed the trailer in, so I went to the bigger ones. Makes the job so much easier.
I put a concrete block at the back end, so when I back in the block stops the trailer from going off the back end and it acts like a wheel chock once parked.
I also got the two rows level side to side with each other so the trailer is level side to side.