There are no mud terrain tires for 18's that will fit (from what I have seen) I couldn't even find a good tire to have studded, they all seemed to have too thin of tread. Get yourself some cheap steel wheels for winter/offroading.
2001 Ironman Daily Driver... 3.5" suspension lift (OME912 springs and 1" spring spacer), ball joint flip, 1.5" front diff. drop, 33"x12.5 TrXus MT, 16x10 Eagle Alloy rims, Interceptor, PV muffler, K&N air filter, Alpine Supercharger, Bilstein shocks, and some trimming.
2000 Ironman Project LS-1 VX... very slow progress but someday....... ohhhhh someday......