the penetration enhancer is octyl salicylate. The liquid is fully oil mixable. In a study of topical finasteride, they used 0.025% finasteride, 25% propylene glycol, 50% ethanol, and 25% water. 0.75% of the finasteride was absorbed. When they added I think 10% octyl salicylate to the mix, finasteride absorption increased to 7.5% of the applied amount. Finasteride and spironolactone are both steroids, and look similar. They both have similar solubilities too. So I think the octyl salicylate should have the same absorption effects as the finasteride. You could just add some octyle salicylate to lipoxidil's spironolactone for better results. 3mL should do. Too much and it won't dissolve.
If you put spironolactone in a liquid by itself, it will probably be stable a month or maybe more. You could make smaller batches and refridgerate them, but I think a cold topical might close your pores and reduce absorption. spironolactone is most stable at pH 4.3. At that pH, it should last longer even at room temperature. I don't know how long, but just that it lasts longer. spironolactone reacts with minoxidil. Caffine also reacts with minoxidil. Keto and pirotone olamine both are most stable around pH 6. So if you mix spironolactone with them, it is hard to make both last long. Copper peptides are also most stable at pH 6. Most shampoos are pH 5.5 or 6, but you can't mix spironolactone with the peptides and expect both to last long.
I don't know how to make shampoos penetrate better, though I guess nizoral penetrates very well. I add a little propylene glycol to my babyshampo.
The common sense preservation methods I'm sure you could think of are to make less at time and store it in the fridge. The way to adjust the pH is to add something acidic to the shampoo in the right amount. I don't recommend adding it to nizoral, since lower pH could damage the keto. But I can take some babyshampoo to the lab and see how much synthetic lemon juice is required to lower 8oz to pH 4.3, then tell you. Vitamin C actually buffers right there, and would be therapudic. The problem is even with BHT added, a solution of Vitamin C is very unstable, and actually breaks down to for free radicals in 1 week tops. Sounds far fetched since I've seen sun blocks that have vitamin C, but Old Baldy has read this many places. So I'm just playing it safe and not using it.
I still want to maybe grind some vitamin C up every few days, mix it in water, drink most of it, and put 1mL on my head. I'd be careful to make it dilute though.