I always bathed with Madison when she was a infant, even at home. Like isla bonita, we used the plastic bathtub once and that was it (well, okay, we actually used it 3 times, but then never again). I'd try to bathe with her when my husband was home, but when he wasn't I'd do the same thing, bring her travel swing in the bathroom with me, let her swing while I showered, then I'll fill the bathtub, bring her in the tub, then put her in her towel in the swing while I got out.
On vacation we did the same thing most of the time (we even brought the travel swing). We also bought one of those sponge bears and used that for our first WDW trip when she was a little under 3 months old. We put the sponge in the sink and bathed her on that if she didn't come in the tub with me (sometimes my SILs or cousins would bathe her while I showered to save time). Since they harbor bacteria we'd throw it out at the end of the trip (we got them a few times).
We have an inflatable tub at home that I use often now since I don't bathe with her as often. Madison loves the inflatable tub and I think it's so much easier than the big bathtub because you can lean them against the back to wash their hair, plus if they slide it's a soft cushion they crash into, not the hard tub wall.