Any skill requiring grenades is really problematic on silver/gold. You simply can't camp an ammo box.
It's too much of a liability.
It's not about the camping, it's about the resupply rate... it's much slower on silver/gold.
With that said though, that's what all those thermal clip packs are for. For some reason, the game decides to give me so many thermal clips that I've got over 35, yet only about 4-5 each of launchers/gels and ONE survival pack.
I've been levelling up a Drell Adept lately and you best BELIEVE I'm spamming grenades in later waves on Silver.
Btw, Drell Adept... great fun. Reave/Pull are not quite as strong as the Asari's Stasis/Warp but Cluster grenades are strong, can be upgraded to throw 3 shrapnel and can also detonate biotic explosions. Too bad he's so squishy, but Reave helps out there a bit.