I had that hardcore in summer 2007 as a result of antibiotics I took in summer 2006. For not absorbing moisture, have him try Glaxal Base cream. It comes in a big white tub, label in greenish/blue and white, you can buy it at Superstore. After he takes a shower, very very lightly pat down with a towel then apply the cream (the more water there is, the better)..the water drying helps the skin absorb it more. Then he should just let it all air dry, it's quite a process, but it can be worth it.
My dad also told me to put cream on and saran wrap the worst areas to keep the place moisturized..then go to sleep... it did wonders for my skin.. my eczema was usually the insides of my elbows and backs of knees. Calendula cream and Aloe vera CREAM (from the states) are good basic moisturizers throughout the day. In times of dire need, I've also gotten simple Zinc Oxide baby creams (usually used to treating diaper rash) and that's worked. It also sounds like he's built up somewhat of a tolerance for his creams/medications so maybe switching up the creams every 2 weeks can help. Sometimes I just had to put off using my cortisone cream cuz I noticed the more I used it the less it seemed to work, so I started switching it up and not putting on the same medicated cream everyday.
There might be days where he has to deal with the itchiness but you can get PEPPERMINT BODY LOTION for that from places like Planet Organic (Coq) or Nester's Market (Vancouver) and that's just infused with peppermint oil and it will help TREMENDOUSLY with itchy, reddened skin! It makes you feel all cold/tingly
Maybe you guys should try a naturopathic doctor? My ex and his bro were really allergic and they just took a different type of test where they just waved something over your finger and did a reading analysis or something.. (not the pricking test that I had to take) and it turns out they were allergic to all sorts of things, like white rice, wheat, dairy, etc.
Also remember, people's bodies change every 7 years. So possibly, the things he was allergic to back in the day isn't what he's (becoming) allergic to today.
I was allergic to seafood when I was a baby. When I was 15, I found out I'm not allergic to seafood anymore but now I'm allergic to cats. Which would have been a good thing to know since I was suffering for 3 years unknowingly cuz I acquired a cat between that time period. And now, I'm not as allergic to my cat...I'm allergic to chicken. My mom also can't use fabric softener in the wash, since my skin is so sensitive..so having that stuff touch my blankets/tshirts etc. will drive me nuts.
Omega-3 Fatty Acids (Fish oil), Acidophilus, Evening Primose Oil taken orally (can be bought at various health food stores) can also help. Not immediately, for remedies taken orally, it should take a while since it needs to build up in your system first, so if he does that, don't expect a clear result until a month or so later.
Anyway, hope some of that stuff helped. I hope little man gets better soon