Thanks for all the feedback, it is exactly what I need to make it better.
After all of the comments on the stability in the long run of the 3' box I'm going to add some diagonal supports on the bottom to make sure it never moves at all. If it were only me going on the ramp I'd probably say fuck it and just not worry about it (it is really strong, I would feel safe jumping on it repeatedly), but it's not only me going on it. It's going to be friends too and I wold feel terrible if something happened.
To reiterate, the sawhorse is Extremely temporary
as in tomorrow I'm making a replacement. my friend had to stabilize it until he took the picture. It is not safe at all.
One of the things I am most proud of is figuring out how to attach the ramp to the platform. It is definitely not just drywall screws.
These pictures are from the top box, and it shows 3 2x4's with 1 1/4" holes through them
This is the top of the ramp with 4 2x4's with holes drilled through them
this is the 1 1/8" dowel that goes through them to lock them together.
I really went for overkill on the strength of this. The pieces connected to the ramp have a minimum of 5 3 1/2" screws. The only thing that could be worse than the ramp collapsing would be the whole tower collapsing.
Really, thanks for all the help guys. Every piece of advice that you guys give me is one less trip to the hospital this winter