Thanks for the detailed post KC.
The Trap Guard I found on my own. Same with the Timbren Axle-Less Suspension. I looked at pictures of trailers then designed what I wanted, searched Google for things to work the way I wanted them to (like the trap guard and axle-less suspension) then went back and looked at build blogs and videos and modified what I knew wouldn't work right off the bat and moved forward with what I thought would. I'd planned on hiring a professional trailer designer/builder or mechanical engineer to assess my design to avoid the unforeseen problems you've described. While not a math and science girl by nature I've learned at least the basic concepts of things like the moment of inertia and fulcrums and such by watching Mythbusters on tv. So while i'm nowhere near an expert on such matters, the good thing is I'm at least now aware that they exist and needed to be considered in my design by someone who knows more than I. Even knowing it's best to balance the interior load is something I was aware of so I came up with what may be an original idea that I think will work very well. By moving two small cabinets and bolting them to the opposite wall during transit, I can keep my weight balanced. And do it easily if I keep those cabinets on casters, which is good because the height of the casters will allow me to open the cabinet doors even with my sleeping pad out. It's all very carefully planned.
To answer your question, no, I'm not a professional or experienced welder. In fact I just took my first MIG welding class a week ago and a basic metal shop class last night where I learned how to use a cold saw, vertical band saw, horizontal band saw, drill press, bench pedestal grinder, and a disk sander, all to make an aluminum bottle opener. I have a lifetime membership to a place called http://techshop.ws/ which is like having a gym membership but instead of exercise equipment it's all industrial arts oriented from traditional equipment to CNC. There's a wood shop, metal shop, TIG and MIG welding, industrial sewing machines, laser cutters/etechers, 3d printers, powder coating, even a water jet and more. They offer classes, one on one training, and dream coaches. So, I want to undertake learning to do it all. I'm not concerned about how much time it will take to build things because right now I have the luxury of time to go in and practice and work all day for the next few months.
I figured I'd take on a few small tube welding projects to hone my skills before I tackle my trailer. For starters I think I'll build a small backyard chicken coop frame for my friend who wants one and a 50% scale (2'x3') of my trailer that I'll use as a dog house for my dog before building my chassis. I can also have a professional welder check my welds along the way to give me the go ahead that my welds are done correctly and will be road worthy.
Thanks Bogo. That sounds simple enough as long as I can detach the hose because I had the sink in one of my movable cabinets. Do you think I could set the PVC into the wall then clamp a short section of flexible tubing to connect the tank to the PVC? That would make it easier to disconnect during transport if I stick to having the small tank in cabin. Based on my initial idea to just have a 1.75 gallon interior tank this was the design I came up with;
I was just going to keep fresh water in a vessel like a small pitcher near the sink. For overnight trips it would work perfectly to have the small tank size. But, if I do begin taking longer trips then the larger exterior tank would be a very good idea if the trailer can take the additional weight of the water until I can dump it.
I'm just trying to be encouraging.)
Fred 
