Strategy for Rider/Berserker BP3 with a Caster-heavy team

So far in this event I've had reasonably solid results running two Wavers(mine is currently 5/8/3), Hans(1/2/1), Mash(6/3/3), and Cu Chulainn(2/8/1) with Jack(10/1/8) as a main DPS. Today, I'm finding that the Rider minions are killing my Casters too fast for me to survive the full 15 turns. Presumably, I'll hit the same snag on the Berserker days, although they should be much easier to AOE down with Santa Salter or something. If I burn Jack's NP turns on clearing the hands, I run a real risk of losing her to Ibaraki damage before she can knock out 1.5 million DP. I'm F2P and short on ascension and skill materials, so maxing out additional support servants like Georgios or Shuten-Douji isn't super realistic for me. Should I grab a friend's Shuten to help nuke the minions? What's been working for y'all?
I realize that I'm not likely to clear 300mil DP, but I'm hoping to get as many materials as I can.
My current lineup goes Jack, Hans, my Waver, support Waver, Mash, Cu. It pulls 2-3 million DP on average, focusing on survival once I've cleared the 1.5mil threshold to make 3BP worth it.
Other event-relevant Servants I own and have at high/max levels include Vlad(7/4/2), Karna(85, 1/4/3), Heracles(NP2, 10/2/1, no bond CE), and Robin(6/2/-).