Dang, I had about 7 pages of response and then hit the alt-b button.
My suggestion for fuel tanks is: get a used tank off of a truck that has the same frame as your bus. That is what I did. The International frames that you and I have are pretty standard medium truck frames. The brackets and tank that I added to my bus were from an old fleet service vehicle that was sitting in a field. The parts *fit* the frame. Huge advantage. Plus you don't have to figure out how to plumb anything, how to install a sending unit for a fuel gauge, or anything. Fuel line parts are standard. Just drill the holes, and mount the tank....almost.
Normally, you install the brackets on the frame, then put the tank on the brackets, then tighten down the steel straps that hold it on. It's really hard to do it in that order under a bus body! I ended up assemling the whole thing and lifting it up and bolting it in place. The placement of your bolt-holes is critical. These brackets had four 1/2" holes each, which meant drilling eight 1/2" holes in a hardened steel frame. DRILL HARD, SLOW, AND USE OIL. Drill in steps, too -- 1/4", 3/8", 1/2". A day's work if you include taking it off the donor vehicle and putting it on the bus all together.
Here's a photo documentary of the process. http://www.skoolie.net/gallery2/v/Skooli ... n/album52/
The tank was installed for my indefinitely delayed WVO conversion. I chickened out on cutting fuel lines that work *right now*. Now that I moved, I don't have a supply of WVO... But anyway...
As far as holding tanks go....here's my solution: http://www.skoolie.net/gallery2/v/Skooli ... struction/
I just tied mine on with rope! Why not? If the application is correct, it's a useful construction material. People have crossed oceans on boats tied together with rope (not that a bus is a boat, or driving 45 mph is the same as sailing the pacific, but the material is a legtimate construction material.)
http://www.skoolie.net/gallery2/v/Skooli ... t.jpg.html
My tank is made from a 14(?) foot long piece of 8" sewer pipe. PVC fittings for the pipe. I used a Spanish Windlass in the construction process, which was fun! The plumbing is all standard household stuff.
The flat discharge hose for my tank fits an agrigcultural quick-release fitting for irrigation hoses. There is a whole bunch of neat bus applications for the agricultural irrigation products. I got my hose parts at Tractor Supply. I don't dump sewage, just graywater, so the flat discharge hose is fine, and it rolls up and fits in my battery box. It also has a standard sewage system 4" PVC fitting on the discharge end, so I can screw it onto a hook up at a campground or RV Park.