3 x 1.8, 4-4.4 (Alpinia and Kerria) and 5.4 damage (its still 3-4 in the current snapshot) knights help alot with Whale Airship missions. Unfortunately you'll need rainbows for these.

Flower Cannon, Howling Cannon and 300% Solar Drive helped a ton and actually required less rainbows to do the Swan Boat missions. They're still hard as shit though unless you have 4 rainbows with evasion on your first team.