ABS lips are a lot less forgiving and you definitely need to be more careful with these. That being said, I just installed my mugen replica that I bought from bayson r.
If you can, have a friend help you out.
If youre starting with your drivers side, turn your wheel all the way to the right so you have space to use your screwdriver.
Screw the top first, make sure you screw as close to the edge/top corner as possible without leaving it too thin (not so close that the screw will crack off).
Turn your wheel all the way to the left. Heres the tricky part. If you just try to wrap the lip around the corner, its not gonna work. In fact, its gonna look an inch or so short. What you want to do is lower the lip right below the bottom of the corner and slide it up. Its not gonna be smooth. It will help if your friend gently pulls the lip towards you to create space. Its gonna take some effort to get it up to the desirable height. When you get it there, have your friend hold it in place while pushing it in, then screw.
Take a step back and see if its even and to your liking.
Uninstall the lip, use 3M red doublesided tape and use it at least in the center. I used about 3" in the middle and 3" about half a foot apart on each side.
Put the lip back on and install the other 2 screws.
Hope this helps.