An interesting study here suggests, unsurprisingly, that demodex mites like to live in the ear canal, and that steroids can increase the demodex mite population.

https://www.ncbi.nlm.nih.gov/pubmed/25033419

In eczema treatment, it's well known that you need to treat the ear canal when there are relevant symptoms, but in rosacea I've seen no discussion whatsoever of how to treat the mites that are hiding beyond the visible outer ear (a relevant symptom would be for example redness and itching on the outer ear and possibly in the ear canal itself). Unfortunately the treatment for the ear canal in eczema is often steroid drops which is clearly a terrible idea for rosacea (where the demodex mite is likely part of the cause, so you definitely don't want to increase numbers with a steroid!).

If you want to know more about ear eczema, google "National Eczema Society, ear eczema", they have a very useful PDF, but it's not possible to provide a link to it - it's downloadable.

There are actually a lot more treatments for ear demodex mite conditions in dogs than people.