Teardrops n Tiny Travel Trailers

Not a foamie, just hoping you out of the box thinkers can help me.

I am designing a 3.5 by 7 foot trailer. This would serve as a base for a tent top. The walls would be about 14 to 16 inch. The idea is to build the box with hinged flaps for a lid then when opened up put a tent on top.
I am doing this to have a roomy 9 by 7 area, decent beds on both sides, ability to stand in the center and it would be lite. Also easy to tow as it would only have a very small frontal area.
Weight is a huge concern. With all the gear for 2 people I would like it to weigh about 600lbs. The trailer including the box at 300lbs or less. So I have 300lbs for cargo.
Any advice on the frame design would be appreciated.

I was thinking of a modified pico lite frame. Using angle iron and making it shaped like a boat trailer. I would put a piece across the back then about 2 or 2.5foot from the back. The sides would angle in at about 4 to 4.5 feet from the back to form the a at the front, no one would be standing within 2 feet or so from the front of the box.
The 1/4 inch plywood sides would would.be glued and bolted to this angle iron frame which would add strength. The 1/2 inch plywood floor would be glued and screwed or bolted on.

What size of angle iron should I use? A 250lb person will be standing on the floor.
Tanks for any help you can give.

Any other better ideas?

If you can afford aluminum C-channel profile and an experienced designer/engineer that will give the best result.

Just for a nice rigid but lightweight lower chassis frame, the superstructure can then be trial and error.

My goal is also very light weight. If I did not already have something for free (my other goal is very low cost), I would be looking at an aluminum trailer. As it is, I am modifying the lightweight steel frame from a 1988 Jayco pop-up that we scrapped. The Jayco is made mostly from very light C channel, no more than 1/8” thick. I think I can make my mods using old bed frame lightweight angle. My goal is to make a light duty flatbed that is exactly the size needed for the foamie I intend to put on it. I see no reason to use any “normal” weight angle from my scrap pile. Nothing here requires that strength, and I don’t want the weight.

Why dont you use the same kind of platforms that some of the motorcycle campers use. They are very lightweight or as light as you are going to get. I would think that you would need a whole lot of angle iron to support a 250 pound person on a 1/4 inch of plywood. If you start with a small trailer even a smaller harbor freight you could build out over the frame with a folding platform made with 3/4 inch ply and a couple of stabilizers when you open it up. A sheet of 3/4 is about 70 pounds. You would be towing less than 200 pounds.

Well, you could consider going up to a 4'x8' trailer since off the shelf materials come in those dimensions and that is close to your original size.
If you want a very lightweight aluminum trailer, you might look at the Northerntool 4x8 utility trailer.
It is 200 lbs shipping weight, has 1170 lbs load capacity, and is $650 shipped.
I have not used one of these trailers so I cannot comment on its quality, but it gets good reviews.
It is a bolt-together trailer which avoids the problems of welded aluminum but may not be as rigid.