Any tips for this dungeon? I'm guessing high resist + staying power would be the way to go but I'm having a hell of a time with it.
You're on the right track!
Vicious Gaan-Telet is a marathon run, so I think the most important thing is to be very careful about not wasting exploration because you're really going to need it all the way to the end. When exploring the top floor, do your best to move in the middle of the road and stay away from exploring the tiles on the outside walls. The reason for this is because the outer wall doesn't actually have any glyphs, items or shops to find, so it's best to save those tiles for later on and focus on exploring the middle road to find upgrades for your character. Every tile counts, believe me.
You want to head in to the first subdungeon at around level 5. You can get away with level 4 if you're super strong or wait until 6 if you're weaker and want to play it safe. There are 5 enemies in each sub dungeon. When you take your first battle in the subdungeon, you're going to want to use that exploration to locate the 5 enemies before returning to the top floor to find upgrades. Do this during a regen fight or after the fight to replenish your health and mana. The reason for this is, say you just finished a fight and want to heal up with top floor exploration to find upgrades. What happens is when you go back down to find the next enemy to fight, you are already fully healed and are now just wasting those tiles. When you do find all 5 enemies though, you can resume top floor exploration to heal up or regen fight and treat the rest of those tiles in the subdungeon as you would the outerwall tiles on the top floor. It also helps to see all 5 enemies so you can choose the best order to fight them in (save poison/manaburn enemies right before level up, etc)
I suggest trying the Dwarven Rouge again. That was my first victory in VGT and it was the simplest (still very tough!) Prep Taurog as a good piety farm. Try to get his blade early and at least his Armor for the physical resists before you switch out. Glowing Guardian is also good for a Dwarven Rougue. Your first god should be one that brings in a lot of piety for the Pact Maker and Dracul. As soon you find the Pactmaker, get Body Pact. The earlier you find it the better your chances of winning. You really really need the resistances. The enemies you face just keep hitting harder, so the resistances are really going to help. The reason your first god should be a good piety farm is because as awesome as Body Pact is, it eats up a lot of piety. You're going to want to keep earning piety after Body Pact for when you eventually convert to Dracul. Dracul is the best endgame god and almost always necessary in VGT. He sucks as a piety farm though so try wait on converting until you either max out on piety or you run out of resources. If you want to get fancy switch to Tiki Tooki before Dracul for another 10% dodge. This 10% can help a lot.
Prep Dragon Shield. The rouge's damage is already really good and his health will be good enough late game, so instead of the gauntlets I take the Shield because what you really need are resistances.
Try not to waste too much popcorn because you're going to need it as curse fodder. If worshiping Taurog, kill magic attack/undead popcorn first. Magic for the extra piety and undead because you don't want that around as popcorn when you're worshiping Dracul.
Each class has unique challenges in VGT of course, so coming up with a good plan is very important.
VGT runs are always epic, so have fun with it
It can be tough to get used to and you're going to fail a lot, just try to always figure out what you're doing wrong and how you can improve. Keep trying, it's worth it! Victory in VGT is very, very awesome.
edit: Another thing I like to do is prep a burn salve and fortitude tonic. The golden statue is going to weaken/corrode you and you're going to get weakened again when you fight the illusion. You really need both of those. If you're lucky you will have already found Earthmother so after you kill the statue you can desecrate her altar for 30 piety then use the burn salve.