Weezing is one of the better physically defensive tanks in Generation 3, the other most notable one being Skarmory.
Skarmory is generally the better option, as it has access to Spikes and Whirlwind. However, Wheezing is still a solid option. His Poison typing gives him only one weakness (with Levitate). He has Haze. Also, he has access to coverage in the form of Flamethrower, and is therefore rarely completely walled.
His stat spread is pretty good, as well. 90 Attack and 85 Special Attack will give decent power to any moves you choose for him.
His low health is a problem, but Leftovers and Pain Split will help keep him alive.
In my experience, Wheezing can be great. Just keep him away from Special attackers.
This set (from Smogon) is good:
Weezing @ Leftovers
EVs: 252 HP / 252 Def / 4 Spe
- Sludge Bomb
- Pain Split
Personally, I'd put your EV's:
4 SP. ATK
With a Modest nature.
OK, that is generally how you should use Wheezing. Shut down Physical attackers, and troll everyone.
To answer your question, then, put the EV's into health.
sumwun is completely right, Will-O-Wisp is pretty much mandatory on Weezing. As long as you can breed it onto him, the fourth move has to be Will-O-Wisp. Plus, Sludge Bomb has a chance to poison, anyway.
Since this isn't an actual competitive format (I am assuming this is ingame, battle tower, or battle frontier) Double Team is legal. It's a decent move for him, and his bulk gives him a chance to set it up. However, without further investing in attacks, he will be out-stalled eventually. Umbreon with synchronize WILL give you a problem.
Just thought I'd add this:
In-game, always boost his special defense. Competitive, he needs as much defense as possible to do his job, and shut down physical sweepers.
Thats all, folks!
Hope I helped...