I did the same a few years ago, gravel pad for the trailer. A couple of considerations are underground utilities and weeds. Call the "dig" number, lots of areas use 811, and they will come out to mark underground utilities. The city thought I buried a storm drain access, but I was able to show them the access about 6 feet off of where their map placed it. I also found out there is a gas line under my pad. I still would have done it, it is just good to know. I had to move the trailer for them once when they were working on the line. My first thought for your project was any sewer clean out next to the house, you dont want that buried. Next is weeds. I had to make a frame out of pressure treated lumber for two sides to keep the gravel contained, and not have it wash out during our WA rain storms. I poured larger gravel as a base, then small gravel as a topping. It really has solidified well. I have some weeds, but they arent coming from below. Seeds blow around and land then grow on top of the gravel. Bottom line is that I am really happy with the outcome. It isnt perfectly level, it stll has to drain, but the fridge works, and I am not parking in a mud pit.
