I suffered the same problem, with the same model, the ice built up underneath to a thickness of over an inch from the seal of the freezer door back to a depth of 8 inches approx. Inspecting a similar one I relaised the foil insulation on the base of mine had deteriorated over time to such an extent that very little of it was left. As a corrective measure I lagged it with foil bubble insulation, a piece of which I obtained from work. I taped it on with foil tape. Problem solved, hope this is helpful, assuming the same problem
Electric_AL
May 2006