Im having a hard time getting 2 upgrades on GP ult

lets look at this gp top/mid has just over 200 creeps at the end of the game on average http://champion.gg/champion/Gangplank/Top IF he gets all 200 of those on a max rank q, he gets 1600 serpents, all 3 upgrades. now lets be real, that is impossible the early game you have less gold on q, so thats less. also, a huge chunk of those creeps, especially early, wont be from q. if you spam q, you run out of mana fast, not to mention the cd early. right now im getting around 900 on a good game, so i can almost get 2 upgrades, but its getting to be really hard. by the time im able to just barrel and one shot an entire wave, its me and my allies 5 manning mid and going into teamfights, i dont have time to farm my q. I dont know what the solution is, but im having trouble with it.