The 4 (2 per side) webs you added to support the thin band would be greatly improved if you also had a tube in there.
In terms of point loading, those two tubes plus the one centered would probably support a bumper. The webs would fail if ever directly loaded.
The entire angle gusset you’re making is a bit inefficient, but as long as you understand the pros/cons there it isn’t the end of the world.
there is enough space to fill the area of the web around the 2 center wheels with tube along the angle, this plus the above suggestion would really frame that out and make it far more robust. If this was all 1/16" wall tube (which is easily could be for this support) it’d be plenty strong.
Another option is to put a support between each wheel (3 total), and not connect them at all. They don’t need to be connected per the rules, and the connection (as you’ve done it) doesn’t provide really any meaningful strength.
Keep it up though! I like the use of colsons.