What you need is a nonpenetrating mount. It is a base where you can put solid blocks inside of it and it will hold a dish even larger than the one you need to use. I put one of those on a roof years ago and it is still there. They are using it to hold a wildblue dish now but I had installed a weather satellite dish up there at the time.
The windload of a 36 inch has 8 times the windload of an 18-20 inch dish.
The windload of a 36 inch has 8 times the windload of an 18-20 inch dish.