Some ice on the evaporator is quite normal. You always get some humid air in there when you open the lid and stored items are adding to it as well. It shouldn't be covered in it though.
Adding a small circulation fan (parallel to the condenser fans, so only running when compressor runs) helped mine run more efficiently and reduced ice buildup.
My fridge came with seals, although they were black with mould and falling off, so I replaced them with an adhesive backed foam strip on the lid and a plastic-backed foam strip on the fridge side, that form a good seal together and still permit the sliding action of the split lid. There is a thread about this somewhere on here.