My thoughts on Mega Camerupt for Trick Room:
While Mega mawile is undoubtedly powerful and can tear unprepared teams apart, it also shares its typing with the premiere TR setter, Magenera, and stacks its fire and ground weakness. For this reason, TR teams tend to have a nasty fire weakness in general, and have few switchins for hard hitters like Mega Charizard Y and Victini. The most common TR fire resist seems to be Marowak A, but because it's also weak to all forms of hazards, and most TR teams don't run hazard control, Marowak can't consistently switch into to fire moves. Offensive water types like Azurmarril and Crawdaunt fear Grass coverage moves and burns, and slow/powerful Dragons like Dragalgea and Drampa have a hard time breaking through defensive cores with Steel types, and are subpar picks.
I've run bulky band Tyranitar on TR, and while it is effective at removing Mega Char Y from play, and can sweep with Band boosted Stone Edge, locking itself into any move, especially Pursuit, can be an unattractive prospect on a playstye which thrives on momentum. Like Azurmarril and Crawdaunt, it also mislikes switching into Will o Wisp or Lava Plume Heatran, as a burn makes it dead weight.
So, to me the main benefit of Mega Camperupt over Mawile or Marowak, is that it is a burn immunity/fire resist that is SR neutral, and still maintains impressive offensive and defensive capabilities.
Its low speed, typing and coverage are not unlike Marowak and it's even a proper electric counter, like Lightningrod Maro, but doesn't have to take recoil from its most powerful STAB. Its speed is also lower than Marowak and Mawile, so its able to run through Toxapex, without being underspeed, and can OKHO with STAB Earth Power.
While it can't boost its attacks like Marowak, its Sheer Force boosted STABs still hit like a truck, as does its coverage moves like Ancient Power, which is handy for taking out mons that resist its STABs, like Charizard Y, Dragonite, Salamence, Gyarados, Pelliper and Mantine. Eruption at full power is an especially strong nuke, and makes it pair naturally well with Lunar Dance Cresselia, who is immune to its ground weakness. Other options Camerupt can use include HP Ice, handy for hitting Zyguarde and Garchomp, and the aforementioned Dragonite and Salamence.
If used with Tapu Bulu, Grassy Terrain can enable Camerupt use Nature Power, for a Sheer Force boosted Energy Ball, handy for taking out all nature of water types, including the troubling Rotom W. Grassy Terrain is also handy for the camel as it protects it from Earthquakes, provides passive recovery, and does not inhibit Earth Power's damage output.
Finally, if the player doesn't want 4 attacking moves, Camerupt can always opt to run Stealth Rock, which is always handy. Mega Sableye also has a hard time walling it, and can't burn it or Knock Off its item.
All in all, Camerupt is a solid TR pick. It gets hard stopped by Chansey, but Taunt SD Tapu Bulu is a great stall counter anyway, and a good teammate for the camel.