the fact that he was a recruit in the navy implies the family wasn't that rich or important, certainly well off compared to the your average person though.
Thus do you think that he and his family belonged to the Egyptian "middle class"?
I just want to point out a thing: in the letter he talks about a possible promotion; I suppose that few recruits might hope for a promotion.
In every case it always depends on what kind of promotion... (p.s. sorry for my english)