I HAVE to use a tub to maintain humidity here in Minnesota for my blood (p. brongersmai), there's no way I'd be able to hit even 35% humidity regularly with a glass aquarium-type cage in MN winters.
I find that tubs hold heat better than glass as well.
However my favorite thing to house bloods are plastic commercial cages (such as animal plastics cages) that are 12'' tall, once a blood python is big enough for such a thing. I'm able to control humidity by switching out different size water sources (medium sized ceramic dishes all the way to good-sized tupperwares). As long as they aren't taller than 12'', they hold humidity very well.