What you have is a solid build in terms of power selection and order, though understandably enough it doesn't take into account the improvements to Invul's resistance passives. RPD and Tough Hide now have defense debuff resistance, so I'd recommend finding a spot to fit in RPD. ResEn now gives end drain resistance, so you might want to make room for it, too, but IMO it's not quite as critical as getting RPD.
What do you want to accomplish with IOs? Probably the most popular IO build for Invul these days is the defense soft-cap build, as described in Call_Me_Awesome's guide, here:
http://boards.cityofheroes.com/showthread.php?t=126983
In addition to the recommendations in C_M_A's guide, I'd also suggest slotting your three PBAoE attacks with 3 slots of Eradication for the E/NE defense bonus. (You can round out the slotting with 2 or 3 slots from another set.) That way, you should be able to soft-cap both S/L and E/NE defense.
If that's the direction you want to go, post a sample build and we can give suggestions from there. If you like an IO build with a different focus (Recharge, Regen, etc.) say so and I'm sure someone--or several someoes--can make recommendations.
My Characters
Knight Court--A CoH Story Complete 2/3/2012
Dont know about IO's, im not that rich 
But for slots:
24 => Boxing ==> Dam(24),Dam(45),Dam(46)
Ditch the 2 slots, redraw is bad and u have enough attacks to make a cycle.
Temp Invulnerability ==> DamRes(1),DamRes(5),DamRes(5),Rech(7)
Typo on the last slot? I asume this should be end-red?
41 => Ring of Fire ==> Dam(41),Dam(43),Dam(43)
Same here, ditch the 2. You mainly use this to immobilize stuff (like a AV). Acc or rech is enough.
01 => Sprint ==> RunSpd(1)
If you keep this running, mind that this funny enough can be a end-hog. End-red would be imho saver, max out nett end-recovery 
Mind is quite similair, however i dont pick epic powers except RoF, i went for buildup and weave. (ranged might be a issue, but i always got my vet and RoF).
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
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With IOs, as suggested earlier, it is a very good idea to aim for Defense set bonuses. On top of that, any regen, recharge, +HP and +recovery will be very useful.
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
I have a VERY old Inv/Axe tank that I have not touched in quite some time. He goes many issues back. Hell, he's not even slotted for IOs. Could anyone here offer an advice on 1) how to improve this build. 2) Which IOs to slot up with? Much appreciated. This is his current build as it stands:
+---------------------------------------------
+ Built with SuckerPunch's Online Planner
+ http://www.cohplanner.com
+---------------------------------------------
Name: Avatar of Ares
Level: 50
Archetype: Tanker
Primary: Invulnerability
Secondary: Battle Axe
+---------------------------------------------
01 => Gash ==> Dam(1),Dam(3),Dam(3),Acc(46),EndCost(46),Rech(48)
01 => Temp Invulnerability ==> DamRes(1),DamRes(5),DamRes(5),Rech(7)
02 => Dull Pain ==> Heal(2),Heal(7),Heal(9),Rech(9),Rech(11),Rech(11)
04 => Beheader ==> Dam(4),Dam(13),Dam(13),Acc(15),EndCost(15),Rech(17 )
06 => Combat Jumping ==> DefBuff(6)
08 => Unyielding ==> DamRes(8),DamRes(17),DamRes(19),EndCost(21)
10 => Taunt ==> Rech(10),Rech(19)
12 => Hurdle ==> Jump(12)
14 => Super Jump ==> Jump(14)
16 => Health ==> Heal(16),Heal(21),Heal(23)
18 => Invincibility ==> DefBuff(18),DefBuff(23),DefBuff(25),EndCost(25)
20 => Stamina ==> EndMod(20),EndMod(27),EndMod(27)
22 => Swoop ==> Dam(22),Dam(29),Dam(29),Acc(31),EndCost(31),Rech(3 1)
24 => Boxing ==> Dam(24),Dam(45),Dam(46)
26 => Tough Hide ==> DefBuff(26),DefBuff(33),DefBuff(33)
28 => Whirling Axe ==> Dam(28),Dam(39),Dam(39),Acc(39),EndCost(40),Rech(4 0)
30 => Tough ==> DamRes(30),DamRes(33),DamRes(34),EndCost(34)
32 => Unstoppable ==> Rech(32),Rech(34),Rech(36)
35 => Cleave ==> Dam(35),Dam(36),Dam(36),Acc(37),EndCost(37),Rech(3 7)
38 => Pendulum ==> Dam(38),Dam(40),Dam(42),Acc(42),EndCost(42),Rech(4 3)
41 => Ring of Fire ==> Dam(41),Dam(43),Dam(43)
44 => Fire Blast ==> Dam(44),Dam(45),Dam(45)
47 => Hasten ==> Rech(47),Rech(48),Rech(48)
49 => Fire Ball ==> Dam(49),Dam(50),Dam(50),Acc(50)
+---------------------------------------------
01 => Sprint ==> RunSpd(1)
01 => Brawl ==> Dam(1)
02 => Rest ==> Rech(1)
Thank you very much.