I've been having a lot of trouble with this one... I'm trying to get to at least 40 flags for an achievement on Xbox Live, but so far the best I did was 38. I was so close, but 2 Jacks went off at the same time (Just... horrible luck right there) and demolished all 6 of my Gloom-shrooms.

I suppose I could try the same thing again, but I was having a lot of trouble throughout the game to begin with, so I wanna ask... Does anyone have a nice build that's simple to use, and could pretty much guarantees me 40 flags? I'm also having a bit of trouble in the beginning. I've tried 3 times so far, but I can't really get past 4 flags because the zombies eat through all my sunflowers before I can get a few Pumpkins up.

I'm a good player by the way, I've just never really done Endless Survival before.