The diaper area exploration is just that probably. She's exploring a new part of her body that she is now coordinated enough to reach and it feels good, so she wants to touch it. She'll outgrow that. We simply told our (now 22 month old) daughter that we only touch that part of our body when we're alone at home. As she gets older, we'll talk more about it, but she doesn't grab herself in public or stick her hands down her pants and that is really the goal for right now. If she starts masterbating at 4, that's fine with us! :)
My daughter also has eczema and we've found that cetaphil does help as a daily maintenance when it's not all flared up, but when it's flared up, lots of naked time and a little direct sunlight help a lot. The sunlight does seem to help the most when the affected area is getting sun, rather than just the areas that don't have eczema. We walk outside to get the mail or go for a 5 minute walk around the park, that kind of thing 2-3 times each day and that does the job. If she has on sunscreen, then we go play a the park or things that take more time, but still get sun on her. My MIL is a physicians assistant and she suggested sun exposure to us last year and it worked like a charm all summer and most of the winter. I'm not sure if a full spectrum light bulb would work the same, but it might be worth trying. We also found that fragrance free neutrogena hand cream (http://www.neutrogena.com/econsumer/ntg/productdetail.bro...) helped this winter. It's really thick so we only put it on the affected areas after bath, sometimes at diaper change, and before bed. It definately helps! Our pediatrician advised us to only use fragrance free products because of the eczema. We use cetaphil or California Baby wash in the bath and threw out the Johnson's and Johnson's because that was making it much worse. Hope that helps and if I can be any more assistance, please e-mail me!