Hello Booters. I have just been looking at your post on this very subject from Wed Dec 27, 2017 and thought that weewee's suggestion of Corona ointment sounded like a great idea. I have not seen it for sale here in the UK but as it seems to be for horses, I might be looking in the wrong place!
I get rashes from anything plasticky touching my skin for any length of time, so I try to avoid it as far as possible by putting fabric between the plastic and the skin. Nowadays, most bags come with a fabric cover and, although I don't use them much anymore because I irrigate, they were pretty good at preventing the rashes occurring. Some of the barrier sprays can also help but it's really about experimenting to see what suits you best.
Eventually I gave up with preparatory stuff and made my own backplates out of material that did not cause me rashes, which I then stuck the proprietary bags/sleeves and stuff to. This has served me well for quite a few years and, because they are my own design, to fit my own body and circumstances, I don't have the same problem with leaks and accidents that I used to have before. However, I should add a warning to anyone who wants to make their own. I tried many versions of what I thought I needed before geting to a device that worked properly for me. These things need fine-tuning and I am still in the process of making them better and better each time the next version is produced.
Best wishes
Bill