I suspect these are heaters to stop the fuel from freezing --- or more likely, waxing.

rechauffer here is simply heating, not reheating

I suspect that 'bouche' means the outlet (so as to at least make sure it doesn't get blocked), whereas 'masse' presumably means that the whole tank and contents are heated, to cope with even more severe conditions.

But I must emphasize this is only a linguistic guess, I have no knowledge at all of the subject area!