Where are the rockets for the silverbacks? I'm trying to get the 500 kills achievement but got no rockets. Do I have to have a specific level acquired to unlock the rockets or what? Any info would help
Money counts more in insane horde than in casual. So you'll level up faster on harder difficulties with hard mutators on.
Alternatively, if you know someone who has already got the silverback rocket upgrade you can use their silverback - I did this for two friends last night who couldn't be arsed to upgrade their silverbacks to level 3