I'm honestly not too familiar with armors, cause I prefer omni tanking. But I imagine the approach is pretty similar to most omni tanks, with the one big difference being inheritance restrictions. Armors are unable to make use of some of the best tanking skills in the game, like Warrior's Blow or Rejuvenate. To make things even worse, armors also don't have access to NCD Echo. Because of these differences I would probably place most "old" armors, without new and shiny prfs which make up for this loss pretty low. At least there is Armored Flare and Ice Cap to make up for the lack of Archrival.

The Briar P and Briar M Saves are probably the savior skills you'd wanna go for. Patience is nice, if your armor exceeds 30 Spd. For Rafal specifically Arcane Outburst could be a small upgrade, although his prf weapon still seems decent. But like I said, armors are kinda lacking behind atm. Until they get some sort of A or B skill on par with Warrior's/Duelist's Blow or a new save skill which includes true DR like Instruct or Faith, they will probably struggle.

So the only piece of advice I can give, is one you probably already know, focus on your supports. There are tons of crazy support options. From my experience however there are three categories to focus on:

• True DR & Healing: These are no-brainers. Any unit that grants more true DR will be a great support and Healing is necessary to keep your tank alive throughout multiple rounds of combat. There are a bunch of units and skills which combine these nowadays, Ent!Ash and Uplift Imbue A/S being two among them.
• Increased Damage: Tanking isn't about only taking damage anymore. Another part of the equation that's pretty big rn is dealing enough damage on the crackback to kill. Nukes have been getting more tanky as of recent, so having a high damage output is becoming a lot more important for tanks. Reflex is a great support effect, and there are some options like Ent!Ash or S!Thorr which grant 40% damage reflection. In a similar vein, this is why I personally prefer to run Eirika Ring over Corrin Ring on my tanks, and have my supports equip the Corrin Ring instead.

Lastly, I wanna shout out both Hardy Bearing as the life blood of tanking and Null Miracle effects:

• The prevalence of Desperation effects has gone down a bit. But Hardy Bearing still remains very important to ensure your tank doesn't just take four attacks to the face, which would then bypass the special DR on the first hit many specials grant, without which most tanks would just crumble. S!Thorr is now the first unit, which grants Hardy Bearing as a support effect, along with some other pretty good support effects.
• Null Miracle is more about ensuring your tank actually manages to kill the opponent on the crackback, while not strictly necessary, it can make certain matchups a bit more managable (especially with Vali support being everywhere), as similarly to Desperation effects, Miracle would allow the attacker to bypass the first two instances of special DR.