Every 7 levels you get a free premium box, with a chance of a legendary up until level 70, in which every 10 levels gives you a premium box. At level 200, you get a guaranteed platinum plating, which is a legendary, and is a premium. If you're not happy with that then what's the point of playing a grinding game?
Possible builds:
Yes yes, low cooling, I know, that's the best build I could come up with.
(You can add a Grim Cobra if they try to run away to range 6)
Heat damage focused.
Heat heat focused. (boiler, duh)
Could add another vandal if you feel like it. Or maybe another recoiler. Who knows.