I've packed bottles in cases before with no problem. Hard side cases are better than soft, but so long as you wrap all the bottles in your dirty washing, they should be OK. Wrap them in tied plastic bags for extra peace of mind!
I always wish folks well when they suggest this.
Two occasions I have been at baggage reclaim when cases have come off the belt venting, on one occasion whiskey, on another vino rosso. Not nice.