If find it REALLY hard to level up stormboyz at all... any tips on how to do it?
Barely get any exp per game on them.
search grind maps on steam workshop ... its much faster and easier to level up "weaker" elites this way
Tritol is right. Play some compstomps in 3v3 mode on special maps, designed for leveling. You could download the most popular maps in Steam Workshop.
Thing is they're so weak i find it hard to grind them even on stomp maps
Use wazzmaka with its Q to give a shield to stomrboyz
Same with znapzoging scrap blast wich gives a shield.
Stormboyz will live longer, thus kill more.
Wazmakka will give them more, because Zzapnoggin gives just 225 shield, it's pathetic. Also try to WAGGH! them always for better results, they have more than 300 dps with WAGGGH!
But the best way to make them immortal is "Keep Trukkin" Warboss doctrine. Bring them to fight together with 3 trukks, load them and launch again each 5 seconds. They will recieve shield bonus again and again, this will make them really tough.