I'll try to help, again using your build.
But I'll help explain some more so maybe it will make a little more sense.
1. Our main goal here is Ranged defense. You don't plan on being in melee, you don't have any melee except burn. We're going to forego that as a defense.
2. Ring of fire is being used primarily for the IO passives it is giving us - that being said, it does work with BURN to keep them in it. We also don't care about how long immobilizes, so we went the Thunderstrike route for damage instead of Immobilize.
3. The winter sets are great when you use them for specific bonuses, but just because they're a different color doesn't make them stronger - and they're expensive.
4. We're going to get sets that are focused on RANGED DEF first and foremost. We're also going to go for an assumption that we don't have an incarnate yet, which requires us to slot a little more in defense than we might otherwise have to.
5. Stuffing slots into defensives for very little benefit isn't going to get you to where you need to be. So we're going to move those around, probably to Burn.
6. We're going to address your concern (since I'm not sure how good cauterizing aura is at helping end) by adding some of those slots to Health for some extra Recovery -- and we'll add a chance for heal to Stamina to give a little more health, too, while we're at it. Again, incarnates can be used to help if it is a problem.
7. We're going to move blaster ATO into inferno, because it's pbaoe so has mostly Melee defense bonuses - and we want ranged.
8. We're going to then use the ranged Winter set in blaze x5 because that will give us some ranged defense. Note - you can 6slot Thunderstrike here instead and it'll be cheaper
9. We're going to shift over Blazing bolt to sting of the manticore because A) it gives us ranged defense without 6 slots and B) it gives us 7.5% recharge
10. I'm trying to work within the confines of the powers you are choosing, as I am assuming you are choosing them for your own playstyle. That being said, I did change Melt armor to Burn -- because I just don't see Melt Armor doing much for you as a Blaster.