Very interesting, but rather complex. From what I see, the triangle panels could be equilateral (all sides the same length) which makes the vertical height of the trapezoids 86.6% the slope height of the end panels. Using 45 degree right triangles produce vertical ends, other options are also available.
It is not clear to me how you intend to hinge the panels when the EMT is embedded into the foam. And how do you plan to anchor & seal the plastic living hinges to the panels? It seems like you will end up with an EMT tube on both sides of the hinged joints - could be quite strong but perhaps not light. Can you post a picture of the EMT hinge you plan to use?
I had many of the same aims (low tow height, high open ceiling, 700 lb max) for my 4 cylinder tow project (Tip Top Tear Drop link below). Those are difficult objectives for a first build, especially the weight. And yes, I ended up using EMT in the roof and other places.
For what it's worth, I suggest:
1- Yes, finish your model, it will help a LOT. I would buy some foam board from the local dollar store and keep the first model simple, maybe duct tape for hinges. But don't overlook the play you get from duct tape. Pay particular attention to how panels stack when folded, the foam board should be adequate to reveal folding issues. It is not easy to get real panels to fold flat without creating stress points at joints. For example, consider the hinge between the triangle and trapezoid panels: When opened, the panels align into a vertical plane, but rotates 180 degreses to a horizontal stack when closed. And the end panel needs to overlap them without stressing the top-to-end panel joint.
2- Add up the weights of the major components. One inch EMT is about 2/3 lb per linear foot. That can add up pretty fast! What does your trailer frame weigh? etc.
3- Don't minimize the problem of opening the closed trailer, lift mechanisms are a real challenge.
4- Look over similar designs posted in the Non Traditional section, here is just one similar folding roof:
https://www.tnttt.com/viewtopic.php?f=5&t=64495&start=90#p1230935Good luck, have fun, and keep us posted.