Ah, yes, the nighttime "screaming diarrhea" as I used to call it. I'm SO glad they told you to use probiotics. That was the missing link in my daughter's misery/aftermath of needing so many antibiotics (long story).
I also wish nursing homes/geriatric docs had a clue about this but I'm dreaming (okay, I know that some of them must know about this).
We used a specially made paste for the bottom as well; some sort of barrier cream with zinc oxide, I'm pretty sure. I'll try to update this when I go home, if I can find the name of it (writing from work). But, if I recall correctly, it was made by the hospital pharmacy & may not be commercially available.
Very best of luck to you!!!