I just traveled to Puerto Rico and then a cruise with a Nauticam D810 housing, 230mm dome port, a macro port and dual strobes. I used a Thinktank roller bag, which was fine in terms of flying. Going in, no problems. Coming back, the gate agent pulled my wife aside to 'measure her carryon'. It was a new roller bag which had no problems getting into the overhead. They said it was 2 inches too long (tall?) and forced her to check it. WIth my 230mm dome port inside, wrapped up in bubble wrap.
I managed to get all my dive camera gear (except camera, which I carry in a waist bag) into the roller bag, EXCEPT the dome. That dome is just so big it causes major problems with ... well, with moving it anywhere above water. Packing, carrying, getting it to/from the dive boats, etc. There is no way I could get it and the housing in a carryon. One or the other. Next time I dive I'm traveling alone, so the dome will have to go into checked luggage.
I too have had issues with carryons being weighed. In Auckland they were weighing every roller bag, but didn't force me to weigh my backpack. (My backpack was at least double the carryon limit, but I acted like it was nice and light). In Papeete Tahiti, it was more of a nightmare. There was a 2-3 hour line to check in, and the airport is not air conditioned. As we (very very) slowly snaked through the line, there were two guys at one bend weighing all carryons. I took half my camera gear out of the bag and spread it around. Got past the weight check, and put the gear back. But they had a SECOND weigh station prior to security and after luggage check in. I pulled a similar trick there, but I don't know how I managed to get through.
In the past, I've used a Thinktank backpack (no wheels) and a Thinktank Waist bag (Speed Racer). Although heavy (50 pounds, combined) I at least had the convenience of having both hands free. As my wife and I usually have 3 or 4 suitcases, this is a good thing. I found out how convenient when I had the roller bag and suddenly realized we had 5 rollers (2 carryons, 3 suitcases) but only 4 hands between us. Well, I've now discovered the vast convenience of airport porters and $5 tips.