I love zombies. I love pirates. I didn't have the patience to write separate episodes about these phenomena, so I just chucked 'em together...!
I don't know why the band actually turn into zombie pirates en route to that dimension. There will be some more trans-dimensional shenanigans in upcoming episodes, but there's no more transforming into different things... Inconsistent? Yes. Much easier for me to write and draw? HELL YES.
I don't want to hear any nerds whining about the ship, either. I didn't know how to draw a proper pirate ship. We've got this crappy metal ship thing on the mantel, so I just copied it. So that's a pre-emptive 'eff off' to all you trainspotters...
Finally, just in case you actually care, and I don't get the chance to include them later, here are the names of the Crimson Cadaver's crew (final panel, left to right): Boathook, One-Eye, Chumhead and Deadbeard.
P.S. Just as Mad Dog is the bandleader in their dimension, so is he the Captain of their crew in the zombie pirate dimension. Some things remain constant between dimensions... Like my ego.