My cooker has steel grates. 3/4" flat expanded. Stainless is EXPENSIVE! Season the steel grates with cooking oil and high heat. They'll get better with use, unless you wash them with soap & water after every use. (That's not recommended, IMO). Treat the steel grates just like a cast iron fry pan... Cheers!!!
for the inside of the grill i don't that is a closed grill.. meaning it has doors there is No benefit to using stainless steel grates.. because the grates won't rust on the inside of the smoker because of the seasoning of the smoker. if it is an opened face grill though, stainless steel grates will hold up to the weather better than raw steel.