I started working on this over the last weekend, spent half a day chasing materials and thinking about how to mount the tub to the frame, building fenders, mounting the water tank & pump, etc. I ended up adding 8 gussets and drilled holes in them for mounting the tub to the frame. I plan to run a 2" wide piece of rubber between the tub and frame.... probably not needed, but it makes me feel better. I also added 2 more cross-members and welded in a piece of expanded steel for the cargo carrier part at the front of the trailer.
I wanted to build the fenders out of 2" square .120 wall tube, but didn't have enough material. I ended up using angle iron, which I'm not too excited about. I think it's turning out well and I have plans to extend the fenders forward and will probably do that with 2" square next time I can pick some up. I plan to skin the fenders with sheetmetal and possibly rivet the sheetmetal in place, rather than weld.
I really wanted to start painting the frame over the long Labor Day weekend, but ended up catching a cold that knocked me on my ass Saturday morning. I didn't make any more progress at that point on.... talk about a wasted weekend!
Hopefully this next weekend will be better and I can make some real progress.