Not yet I haven't, any suggestions? Like is the any type of formula needed and how tall should I make the lid open?
No formula. Just prop it open as far as you like it. For me, it was as high as I could comfortably reach.
The people I bought my shocks from said to be sure to attach it as close to the middle of the lid as possible. So, just prop it open and from there, you can figure out where to attach it to the trailer.
If you have visited my thread lately, you probably saw how I mounted mine. I ended up mounting the front one on the outside and the rear one on the crossbar, which you don't have. I'll be interested to see where you mount your rear shock.