I'm not too sure what the growth is, but I may be able to help you with the skin issue.
If Peppercorn does have fur mites, you can get rid of them with Diatomaceous Earth. You can find it at Tractor Supply for around $12 for 20lbs, they may have smaller bags, but I'm not sure. You use it just like flea powder (Leave it on over night though), but it's 100% natural and completely safe (even if your bunny eats it). DE works by smothering the mites, and ultimately killing them. Whenever I have to treat an illness or something with my babies, I do it as naturally as possible, since I've been doing this they almost never get sick.
If he just has dry skin, try using coconut oil as a moisturizer. It works so much better than commercial products, and it's also quite good for the skin. I use it for myself as a moisturizer and use it on my dogs' pads when they get dry and start to crack during the winter.
I have used Ivermectin before but if you do not use EXACTLY the right dose it can have serious consequences. Personally I will never ever use it again (and I encourage others to do the same). I accidentally gave one of my babies a very very slight amount over what he was supposed to get, about an hour later he got very lethargic and had seizures (He got bad enough I almost lost him), after that he always had the same reaction every time he got a dose even though it was the proper dosage. I have also heard of several breeders who lost half of their herds to allergic reactions. Ivermectin even in normal dosages is toxic to rabbits that are dutch marked or have the Vienna gene.