I wouldn't run 20 strong squads, they're awful in melee and easily broken and run down. A generic Tactical Squad will smoke them in combat and run them down. Keep 'em at 10, keep 'em mounted in Rhinos, and only get out when you aren't gonna get charged in return.
I've had great success as long as I've used the rest of the army to keep the enemy off the Troops. As soon as the enemy gets into your Battle Squads you're toast...