We had this exact problem with our little guy. I was going crazy with the rash, and switched him to disposables thinking it would go away, but it actually didn't and got worse.
The things that have helped my ds, now back full time in cloth and rash free, for the first time in months, is changing him every 90 minutes when possible and using Calendula Cream. I use a fleece liner when I'm putting it on him, but I have to use it less and less now as long as he gets changed frequently and gets a little air time.
I also do an extra hot wash/cold rinse with vinegar each time to make sure all the detergent is out.
His eczema was so bad, but the calendual really cleared it up. Kathy