I find that large Warrior squad meatshields in front of Haemonculi is plenty of protection.
I don't use Grotesques in a WWP army at all, because they are almost completely useless in such lists due to the rules for Independent Characters in Reserve. The character can't join a squad 'off the board', so can't arrive on the board attached to the Grotesque unit. Grotesques without an IC are severely hampered, and a turn will be wasted to get an Archon to jump up into their Raider with them, and that's assuming they arrive on the same turn. I've used them occasionally in Raider Rushes, but normally I just stay clear of them.
Besides, breaking and destroying a unit in the same turn that you charge isn't always desirable, if your opponent has spaced his units out sensibly then it will leave your assaulters standing underneath the enemy guns for a turn.. Ideally an assault will last two turns, one assault phase in your turn and then a second in the opponents in which it's won by you - then you can wipe out the enemy unit and have no fear of being shot up because it will be your turn next.