If there are only a few pawns on the opponent's queen side I'd probably be even more cautious, because that means there are open files they can use to attack on that side.
Also, if they have weak pawns on the queenside, then it's likely you can generate play there. If that play involves a pawn break on the queen side (to open some lines against their pawns) then in this case too you likely don't want to castle queenside.
The only real down side to 0-0-0 is that it takes longer than 0-0 and even afterwards the king is still a bit in the center (even if the rook is better than in 0-0). The downside has nothing to do with pawn storms, which can happen no matter where you king is.
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So, a few comments about pawn storms. First, when the players castle on opposite sides (your opponent 0-0 and you 0-0-0) a very common theme is both sides will try to attack the other's king as fast as they can. It can lead to very sharp games where the one who can land the first punch (break open the opponent's king) wins!
If you're both castling on the same side, whether that be kingside or queenside, and you find your opponent is beginning a pawn storm, the best defense is very often to generate some offense of your own. The rule of thumb is to meet a flank attack with action in the center. But in general, you want to stir up some trouble for your opponent anywhere else on the board quickly. Often this is initiated by opening some lines (exchanging pawns).
Trying to use passive defense to directly neutralize a pawn storm can be tricky. If possible, usually what you're able to do is blockade a pawn or two from advancing any further. This may involve the double edged idea of moving the pawns in front of your own king. In general it's much easier to deal with a pawn storm by generating your own play as fast as you can somewhere else.
every time i do it i end up getting pawn stormed and trashed. is it only best when there are doubled pawns or only two pawns on the enemy's queen side?? help pls