2.5 1/4 inch wall thickness will allow a strong back bone with 2 inch access for winch or tow receiver. With 35 to 38 inch wheels and tires I would stay away from any angle on the main frame. Box tubing 2x2 120 wall is your friend. Ends do not twist and allows for a very strong frame. I hate angle in the upper walls, but I am sure you can make it strong enough. I designed mine to survive a roll over so I did overkill in them to say the least.
With drop axles like in your picture, you have several bolts that become very important, normally an air bag and the bounce that goes with it. With the size of wheels and tires you are planning on using, besure you trianglize the frame. brace corners with triangles.
In 45 years of trailer building, from large two car carriers, 5th wheels and toy haulders with FJ Cruisers in them, I have never found a place to put angle iron in any strength situation. Weak, bends and rusts easily. You can get more strength from Box tubing even in the 1 inch 065 wall thickness. And will most likely be lighter. Easier to keep squre.
Have fun, take your time and build what you want. But plan it out, spend a fair amount of time on the plan.
With drop axles like in your picture, you have several bolts that become very important, normally an air bag and the bounce that goes with it. With the size of wheels and tires you are planning on using, besure you trianglize the frame. brace corners with triangles.
In 45 years of trailer building, from large two car carriers, 5th wheels and toy haulders with FJ Cruisers in them, I have never found a place to put angle iron in any strength situation. Weak, bends and rusts easily. You can get more strength from Box tubing even in the 1 inch 065 wall thickness. And will most likely be lighter. Easier to keep squre.
Have fun, take your time and build what you want. But plan it out, spend a fair amount of time on the plan.