Cavilon? When I have really bad rashes on my three year old, that's what we use. If he's only having slight rashes, I switch back to Skin Prep. However, it's not cheap.
If he is actually allergic to the adhesive, try Nasonex. Someone here suggested it, and it worked! I spray a little on the site, let it dry and affix the pod. No more itchies. But I agree with not using alcohol on the whole site. It dries out your skin too much.
The rash stuff is *very* hit or miss. I have noticed if I go to a completely new site (for Omni or Dex) I start getting rash problems again, and then it settles down. I just have to make sure I have enough things in my arsenal to always be prepared for anything. My "arsenal" currently consists of - skin prep and cavilon (barrier wipes), tegaderm and tough pads (physical barriers), and skin tac (sticky and serves as extra barrier wipe).
I just ordered Cavalon too. Fingers crossed!