CONFiture
The wing fuel tank on the B777 goes a long way inboard of the strut.
I can't comment on how often frost is seem while aircraft are landing, but I do meet B777 every day on the ramp at ARN. On arrival on the ramp there is nearly always frost under the wings like on the picture above. The area under the wings inboard of the engine normally shows a clear line where the wing tank ends. Frost under the wings on long haul aircraft is there on arrival at the ramp about 90pc of the year. The air must be very dry for it not to form.