This is an ongoing problem, and I am sure it is me. We started with a cab over camper, went to a 5er, and now have a 29' Type B+. All were new when we bought them. In each case, I have had to defrost...
You say the 'dollar bill' test was good meaning you could pull bill out with resistance?
Heavy frequent icing means warm air is getting it compartment.....either thru door seals, frequent opening of door, leaving door open, high humid conditions.