Ok I'll start this one.......Please... no name calling or cat-fighting here.........
Is the basement still wet? let's try and duct tape a foot square plastic sheet on the floor and on the wall(remove insulation).....several places......tape all edges tight.....What happens in a couple days? If you get 'dew' under the plastic then the concrete is still wet and needs some form of waterproofing......usually applied to the exterior of the foundation walls(before backfilling..Did you do this when you built the addition?)
What kind of insulation? stud wall w/vapor barrier? poured concrete or block? sump pump?
Does the dehumidifier fill w/one or more gallon(s) each day? Other fans to circulate air? Additional crawlspace or basement? Condition?
OUTSIDE: gutters/downspouts/drainage/recent weather/location? where are you/soil type
Post back and we'll get some more answers.....doug