I agree with much of what the other moms have said...I have made the poop goop before at home and it feels weird to put athletes foot cream (or monistat!)on your child's bum but it certainly did the trick a couple of times when he was really bad. Some suggestions though...use just a little bit of the antifungal compared to the other ingredients and make sure to mix it pretty well with the vaseline and desitin so you don't have all the antifungal in one spot. You might just want to buy a jar of vaseline, dump in the other two components and mix with a popsicle stick (which you can then use to apply!)
The BEST thing I found for diarrhea in kids (or adults!) is the peri bottle!! most of us probably remember these from when we gave birth to our little munchkins, but you can also use like a shampoo bottle with a pop up lid (I've seen them in the travel/sample section at Target or Cub or just about any store). It is a squirt bottle that is given to clean vaginal/perianal (hence the name) area so that you don't have to wipe as much with toilet paper when you are trying to heal. Same concept here...fill with body temperature water (if it's too warm it hurts), put your kid in the tub, take off the diaper (and any other clothes you want to keep clean/dry) and bend them over enough so you can get a fairly good high pressure squirt in the crack. If you did a really good job of coating with the poop goop then the diarrhea will wash away without all of the poop goop coming off. The key is to always have a layer of this goop between the skin and the diaper! After rinsing, dab (do NOT wipe or rub!) with some tissue or a wipe or let air dry if you are able to entertain for a few minutes in the tub. It is ok to leave some old goop on there if it is clean. Apply another thick layer of goop to affected areas and put a clean diaper back on! It is kind of a bigger pain than a typical diaper change but so far it has significantly decreased the number of days our kiddo has had a serious rash during these bad diarrhea spells.
Checking the diaper frequently is key...less time on moisture, less time the skin has to become irritated.
Above all: hydrate, hydrate, hydrate. As you know this is pretty much the reason we see kids get admitted to the hospital this time of year...most illnesses can be treated at home as long as the kids aren't dehydrated.
Since you will probably have similar symptoms, the peribottle really cuts down on the irritation of wiping when diarrhea gets bad in adults too. It's like a poor man's bidet. Just squirt until you think that all the diarrhea has been removed and dab with toilet paper until dry.
Best of luck! Rotavirus is going around our daycare this week too so I'm sure that it is only a matter of days before we will also be victims...
A little about me: 27-year-old married mom of a 16 month old boy...almost done with medical school and planning to practice pediatrics!