Agree with everyone else 100% $400 for a level
How I do it cause DW is worthless (shhh, I still love her (didn't say that out loud), but for hooking up or backing and leveling...) I've got this and a backup camera but that's another post.
link here http://images.campingworld.com/is/image/CWI/3000/30939nNEW.jpg?
I can clearly see when backing or pulling into the site and then I can figure by 1 inch increments on the level what needs to happen to level by myself all from the rear view mirror.
It pained me to drill into the fiberglass front but some silicone on the screws and 4 years later no more issues with the DW or trailer fiberglass font.
We are both much happier
Just so you get the idea that level is approximately 12" wide and easy to see from your rear view mirror.
Good luck, have fun and just camp.