I don't use the hooded towels anymore, just regular bath towels. I just set the towel on the floor next to the tub. Then I pull him out and sit him down in the middle of the towel and just kinda wrap it around him while I dry him off. I use a washcloth to dry his hair. Since he hates lying on his back this works better for us. I've never gotten wet doing it this way.
I've never had a problem with him being slippery though. I just pick him by his armpits, how do you do it? Maybe I'm no help at all.