I used to mine gas in w-space just fine in a Venture and later the Prospect, the only ship in EVE which can gas mine in class 5 and 6 wormholes while under fire.
W-space gas clouds don’t deal damage. K-space gas clouds do have a random chance of dealing 1000-2000 damage at the end of every harvester cycle (amount and damage type depends on a cloud and site it’s in). (IIRC if you activate both harvesters on the same tick, you can’t get damaged by both at the same time, so that helps too)
It’s absolutely possible to tank them in a Venture, if you fit it with resistance and passive recharge rigs and modules, and some extenders. And have good shield skills.