They're on aspen so separately for me is more safety than anything else--however, I'm not opposed to feeding in the tub since that's what I did for my newly acquired female because she wouldn't take it in a separate tub, but I had to keep watch and pull off pieces of shredded aspen from the mouse (which had been dried but still stuck) as she was swallowing.

After the initial feeding, it didn't matter where I fed her, she'd take it no matter what.