Another possibility is no armour at all if rune tracing
A thought to follow on here: what happens if the runemage takes excessive damage? Can scar tissue bisect a tattoo and cause it to become non- or mis-functional?
Perhaps there are two variations of runemages: those who use armor and those who don't. The armored mages store a portion of their kremm in the rune to be cast which is inscribed in some manner on a physical object. A physical touch and focused will allows the rune to activate. Once expended the runemage then needs to re-invest the kremm in order to prime the rune again. The advantage here is that an armored runemage gets the benefit of armor protection.
Unarmored runemages inscribe the runes on their skin. No kremm investment so they can have more spell possibilities open to them and an unarmored runemage can cast the same spells at a lower spellpoint cost due to their direct connection to the rune itself. This way a player can choose which direction they want to go and still play a runemage.
I'll have the deep-fried battered pixie with balrog dipping sauce and a Hobgoblin ale.
Also, a thought that just occurred: what happens if a runemage is healed? Can it wipe out their tattoos? I'd imagine that Poor Baby wouldn't do so, being a pretty basic healing spell, but more potent magic might.