for a rear prerunner style bumper with a tire carrier?

Depends if you're gonna drag it over the rocks or not. If it's gonna get banged up, I'd go .120 minimum. If it's mainly for looks, go for it. Even .120 dents real easy on the rocks.

Ok, I checked your profile and it says you have a K5. If this is the vehical that you will be mounting the bumper on, I would recommend using at least .180. IMO, the .090 isn't strong enough for a fullsize.