We're a cloth diaper family here and it can be hard to find a diaper cream that doesn't ruin your diapers.
What kind of diapers are you using? We use mostly Indian Natural Cotton Prefolds, so what works for ours may be different than yours. You don't want to do anything that may default your warranty on them.
I saw someone mention lanolin, don't use that because then that will make your diapers waterproof. You don't really want that on the inside of the diaper.
I also saw someone mention bleaching the diapers when washing. Don't do that either. That can ruin some diapers & if you don't get absolutely all of the bleach out during rinsing that will cause one heck of a rash when your child's urine mixes with it. We learned that from when our son was being cloth diapered and used a detergent that had bleach in it. It was horrible. We have always double rinsed our diapers, but that didn't get it all out in the soaker parts of the diaper.
We use a very simple diaper balm on our daughter. Whipped Shea Butter and sunflower oil. The sunflower oil is high in vitamin e, an emollient and it was highly recommended by our pediatrician who told us about a study that was done with infants receiving sunflower oil on their skin daily made them less likely to get infections. I don't use any eo's/fo's or herbal infusions on my younger children or pets since they can't tell me if it's irritating to them.
Obviously, talk to your child's doctor first before putting anything on your baby. Also, if your baby's rash has any open sores, talk to your child's doctor as well.
Make sure as well that whatever you decide to make that you make sure to use clean containers and equipment, you don't want to introduce any bacteria to the mix.
Also, if your child is getting a lot of diaper rashes or ones that just won't go away, sometimes it's because of the diapers. Like maybe they need to be completely stripped because of urine or detergent build up. Drying them in the sun helps as well. Even in the winter here in Wisconsin I try to get our cloth diapers outside on somewhat sunny days to dry. I usually will have to bring them in and pop them in the dryer a bit, but atleast they got some sun.