Ok, take your ladder run in ramp thing & connect the 2x4's so they are straight.
Here are a couple pics, one is how you have it drawn & the other is the way it needs to be.
Then once that is straight, finish it like your drawing, except don't add the plywood skin over top of the ladder run in ramp thing.
Leave spaces in it, just wide enough so that the front of your board doesn't get caught in the rungs, the fewer the better. Less drag.
Now you are ready to rock.
If whatever doesn't kill you, only makes you stronger.
Then I am so close to immortality