What I did was go to Staples or Office Depot and buy a roll of 1" wide x 8' or so magnetic strip on a roll with the adhesive on one side (under $10 IIRC). Split it into 1/2" wide strips and attach one to the gasket and the other to the matching section on the door opening and that way when you close the door the magnetic strips adhere to each other and provide a seal. The older Norcolds I think used a magnetic gasket, but the new ones for some reason don't ... probably so folks would have to replace gaskets more often for more profit to the manufacturer.
Make sure you clean both the gasket and door area good with alcohol and dry good so the adhesive on the magnetic strip will adhere good.
Larry