My Chasing M2 doesn't have a case, so I've been using my $130 fishing
Cabelas Magnum Tackle Bag for transporting, I take out the trays, just lay the Chasing M2 on the bottom of the bag wrapped in towels for drying it off and extra padding, this tackle box has a sling so it's pretty comfortable carrying it around.
I always try to dry the drone off thoroughly after pulling it out of the water with a towel, of course the towel can't reach the hard to reach places where it's still wet when wiping it down, but that's why I still wrap it still in a long towel of my liking, then lay it down on the bottom of the bag. Afterwards I still get a little water that's pooled up at the bottom, but the towel soaks up most of it. I always try to lay my controller on top of the drone, so when the water disperses, it just gets soaked up by the bottom towel and never reaches the controller.
What was nice about my Geneinno T1, a case was included and it also came with a cable reel, so transporting the T1 was pretty easy. There still wasn't a place for my Ipad though, having side pockets on the Cabelas tackle bag makes it nice for transporting the tablet, along with a few screw drivers, smaller microfibers towel I bring along just in case. I noticed even though the T1 fit snugly in one of those carved out foam spots, I'd see a small puddle of water left behind even after drying it off thoroughly so I know your concern, like what if some of that water makes its way to the controller. You could always try wrapping it in a thin microfiber towel of some sort before slipping it back into the foam. But then it again, it would have to be a very thin towel and considering it's thing, not going to soak up a lot of water. I know these carved out foam spots are pretty snug. You could try setting down one of the microfiber towels in back of the drone before slipping it in the spot, in similar mentality of how I wrap mine before setting it down.
I mean if you find something, let me know, as I was worried about the water seeping over to the other foam compartments where my controller was in the Geneinno case was as well, it never seemed to make it over there, but with time ya never know... And I suspect since each underwater drone is shaped, each drone leaves different amount of water behind on it's exterior body. I mean with the T1 I could dry off more thoroughly then the M2, the M2 has two more thrusters, a lot more hard to reach places where I can't get with the towel.