I've had Preston as a Companion for about as long as he could be a Companion. Naturally, when I got my second set of PA, I put him in it.
BIG mistake. Pretty much EVERY time we go out adventuring, he gets all six pieces of armor trashed. Charge! It's like he feels invincible and must therefore charge into the muzzles of our enemies. The cost in repairs destroyed my stockpiles of Steel, Aluminum, and whatever else it takes to repair PA.
Upon reflection, I pondered why should I provide him such decent armor? He is, after all Essential and can't be killed. And unlike PA, all other kinds of armor NEVER degrade. So suit him up in the best non-PA armor I can find for him and go ahead and let him become a projectile magnet. Better him than me... because I can die.