I decided to follow the advice of commenters Van Hemlock and Jason and experiment with an armour tank on the Rupture. As I had previously focussed almost exclusively on shield tanks I had to buy a bunch of stuff and train some skills but here is what I came up with:
Armour tanking is all about low slots so we have a named medium armour repairer providing ongoing defence and a beefy armour plate adding some depth to the tank. In addition there is an active explosive hardener filling the hole in armours explosive resistance and a passive energised adaptive membrane providing an additional 15% resist across the board. Specific resists can be adjusted to best suit the type of damage expected. The Tech 2 Damage control II costs over 1 million isk but I reckon it is worth it because it performs 2 important roles. It gives 15% universal resist to armour which is as good as having an additional energised adaptive membrane. It also gives a whopping 60% resist to structure which is my insurance policy if ever my armour tank gets overwhelmed. Hopefully this will buy me enough time to warp the ship out of danger.
Two Cap recharger II's fill the mid slots. These are pricey (1.3 million each) but I choose them for a reason. As long as the afterburner is turned off they can just supply the capacitor requirements of armour repairer, active hardener and damage control making the set-up capacitor neutral. This is actually a very finely balanced thing. It only works because my repair skill is trained to level 2. If I trained up to level 3 or higher my armour repairer would cycle more quickly and the set-up is no longer cap stable!
The afterburner is intended to be turned off while tanking to avoid draining cap. It is purely used for getting into position. I reckon it is vital to have though because of the close range armaments on this rig.
I would like to fit long range artillery and heavy missiles on this but I can't. There simply isn't enough power grid. The armour tank modules eat up a good chunk themselves and by filling the low slots they prevent me from fitting reactor controls to get extra power.
I can't fit artillery so I have had to make do with short range autocannons. Two assault launchers should help to kill frigates who have enough angular velocity to avoid being hit by the turrets. Three medium drones add to the overall damage output.
I must admit I am scared that this short range weaponry will get me killed. I need to chase down enemies before I can hit them which makes the afterburner essential. Meanwhile they are getting in free hits while I am flying towards them. It is also much harder to control aggro and line up enemies correctly when you are in the thick of the battle than when you are firing from long range. Perhaps scariest of all is the fact that I will no longer be able to keep comfortably out of webber and scrambler range.
For comparison here is a passive shield tanked Rupture I have successfully used to complete level 3 missions:
At first glance the armour tanked Rupture seems better having higher effective hit points (18641 vs. 17758), higher sustained defence (63 dps vs. 52 dps) and higher damage (125 dps vs. 116 dps). However the Passive shield tanked Rupture uses long range weaponry wher as the armour tanked version needs to be within a couple of thousand metres to do maximum damage.
It is also worth pointing out that the armour tanked version is much more expensive (16 million as opposed to 9 million). That 7 million difference could be used to buy three shield reinforcing rigs which would allow the PST Rupture to out tank the armour tanked version and still retain its range advantage.
All in all I am not convinced the armour tank is actually better but in the interest of science I am going to try it out. I ran it through a couple of level 2 missions last night but it was no real test - the mobs never even got the shield down so I didn't get to test the armour tank. I will take it into a level three tonight and report back. Wish me luck.