Okay, let's take a look at the (red) wizard:
Advantages:
- Spells
- A good will save
Disadvantages:
- Low no. of proficiencies
- Low HD
- Low Bab
- two bad saves
Now, you want to capitalize on your strengths (which you are doing through Red Wizard), and minimize your weaknesses:
Get polymorph. This spell is awesome. Changing into a high con or str form fixes all disadvantages in one casting! Take, for example, the Hezrou:
+14 natural armor
Immunity to Electricity and Poison
+10 Str,
+18 Con
Large size
or the Osyluth:
+11 natural armor
Immunity to fire and poison
+10 Str, Dex and Con
Large Size
Great forms for staying alive*! Now you can't normally change into outsiders, but a recently posted article on the WOTC website changes that so that you can
if you are an outsider yourself. How do you do that? Well, there is the 20th level monk ability, but an easier route can be found in the PLayer's Guide to Faerûn. Under regional feats, there's one called "Otherwordly" which makes you a ntive outsider.
But that's not all: Being an outsider doesn't only mean sweet, sweet polymorph choices, it also grants you proficiency with al natural weapons, immediately removing one of your disadvantages!
*Both a re 10 HD, the maximum you can change into at this level. The Hezrou is good for pure HP and fort saves, while the Osyluth is more nimble, if that's what the situation calls for.