Well, you got me wondering how sturdy my lid is, so I went out and stood on it. I'm 225 lbs. and it didn't move at all. I even bounced up and down a little bit. It seems plenty sturdy!
That has me thinking that unless they serve another purpose, the 2nd row of horizontal frame rails and vertical supports on your lid probably isn't all that necessary. You might could do without and save yourself the added weight, or like I suggested earlier, use that metal up top to support the sheet metal. Again, I'm no engineer, so make your own decisions. I'm only making observations based on how my lid turned out.
ETA.....keep looking until you find a sheet metal fabricator that can make the bends for you. Piecing all that together would be a ton of welding and unless you are a good welder, it will be a ton of grinding and filling too. Even if you have to drive a good distance to the fabricator, it's time better spent...IMO.
wow... pretty cool. now this gives me confidence... i will build the frame following your design then.. if i feel its not going to support after my test by mounting the rtt and couple of people inside i can always add the inner frame later.. thanks dude for the test and observation..
yes i am going to find the metal fabricator.
