One suggestion would be to back off a notch on your volume target, and connect two 2-quart bags to a common hose with short lengths of the same hose and a "tee". The name says it clearly: the "tee" is a hard plastic fitting in the form of a T. Plastic fittings, including "tees", are readily available for use with flexible tubing in a range of sizes from about 1/8"to 5/8" (inside diameter of tubing). The national home improvement centers and most hardware stores of any appreciable size should have an array of them in stock, and Internet suppliers should be easy to find. I also suggest replacing the hose that comes with most bags with amber latex "surgical tubing". Hose of this kind seems to have been standard equipment on the high-end bags of the past. Whereas the original hoses supplied nowadays are usually kink-prone soft plastic (the awful white ridged stuff), amber latex tubing is very supple and kink-resistant. You'd be looking for an inside diameter of about 1/4", not more than 5/16", to fit inside most clamps. Surgical tubing is not as easily found in local retail outlets as the fittings, but there are suppliers that are not hard to find, using -- what else? -- Google. My "ex" and I actually retrofitted her equipment with over 8 feet of this kind of tubing, because the door hook used to hang the bag was a good distance from the bed, where she'd administer. Worked like a charm.
You're concerned about the weight-carrying capacity of your shower rod. Warm water weighs about 8.3 pounds per gallon, so with two 2-quart bags full -- that's one gallon, total -- you'd have no more than ten pounds to support, equipment included. Still, to be safe on the safe side, not having to worry about the rod collapsing in the middle, hang your bag (or bags) near whichever end is more convenient. The closer to a mounting bracket, the more rigid the rod becomes.
Hope this helps, and if I can help you further, feel free to contact me.