I'm in the same boat. I managed to get my Gungans up to R5 a few weeks before the quest started, I couldn't even get past the 1st tier. I upgraded BN and Bomb to R6 with other two still on R5. Managed T1 and T2 but tier 3 was a massive pain in the backside.
After reliciing Boss to R7 and the other 3 to R6 I managed to pass it, T4 again fairly quickly, now T5 I'm having same problem, R1 is not too bad but R2 I cannot get a shot at droideka, I've even got all my mods to god mode and now there's 15 hours to go and it looks as if I'm going to have to wait until the next jar jar release and probably end up R9ing all my Gungans.