I'm thinking about making a Drow Trapsmith as a Sorcerer instead of a Wizard. I like the idea of the synergy that Cha has for UMD and also Will saves with Force of Personality. The question is whether or not I can get away with 18 or even 17 levels of Sorcerer and still have decent offensive casting ability at 20? I wouldn't be skimping on Cha much, if at all, so it really comes down to whether or not -2 or -3 levels of Sorcerer is enough to keep spells from landing on endgame mobs?
I kind of doubt that the idea is feasible but I thought I'd ask people who have tried to get their input on it. Any help is appreciated.