Gilgamesh is dated before the Bible.
Your thesis is unsound. The whole Noah sequence is severely flawed. It had been debunked thoroughly. Go to talkorigins and look it up.
The "written" version of Gilgamesh was certainly "older" than the "written" version found in Genesis. But Genesis was written from the oral tribal traditions of the Hebrews escaping from the Egyptians. Abraham came out of the "Land of Ur" carrying I would assume to be the knowledge of the Mesopotamians with him and as head founder of the Hebrew tribes, communicated those traditions to his son, ect. Who really knows what the older "oral" history was...Gilgamesh or Noah. My bet is is on the Noah story, which was glamorized "docudrama" style in the more colorful Gilgamesh myth!
By the way, though it may seem irrelevant to you...the chinese character for boat...is a boat like symbol with 8 men in it. 8 being the number of men and women in the ark!(the chinese language goes back some 6 to 8 thousand years)