You could try to get an Animated Shield. Animated Heavy Shield would help a lot, and you can then Magic Vestment your armor and shield for an extra point of AC each (no need for Persistence). This would ramp you up to 25. You could get to 30 quite easily. Then you can probably maintain Protection/Magic Circle against Evil all day with simple repeated castings for 2 points of deflection. You could also consider Shield of Faith. Note that you can cast Greater Resistance [SC] which is 24 hours and +3 Resistance to saves.

The other option is getting Monk's Belt, casting Greater Luminous Armor [BoED] for your AC bonus and screwing the Plate. Further, you can use Lesser Restoration to rid yourself of the penalties and then you can Magic Vestment your Luminous Armor. And again, get some Deflection. Oh, and Conviction [SC] should help your saves further. There's no excuse for failing saves as a Cleric.


Spells that might be of interest for persisting in this sense:
Surge of Fortune [Complete Champion] (comes with +2 Luck to basically everything, can be dismissed to Take 20)
Recitation [Spell Compendium] (+3 Luck instead, but no Dismissal abilities or such)

Holy Star [Spell Compendium] will be a nice one in couple of levels. There's also something that grants Morale bonuses defensively, IIRC, but obviously you'll want some offense too (Righteous Might, Righteous Wrath of the Faithful, something of the sort). And don't forget, 10 min/level is easy to make all day.