Well done! I'm wondering if Gyarados would be preferred vs earthquake Donphan because of the resistance. Kyogre gets killed quicker and sometimes with remaining energy. Gyarados is more flexible and can absorb damage to gain energy. Based on my own experience without dodging Kyogre can only use HP twice but with Gyarados safely four times.
Donphan solo
So, I took the advice and powered up a third Kyogre. Below is a marginal team that just manages an EQ Donphan in cloudy weather. 3 sec left. Used only the Kyogres and 2 or 3 Waterfalls from Gyra. Dodged 2 times to be able to squeeze out an extra HP before fainting. Kyogres level 30.5, Gyra level 36.

Answers
Without having attempted a Donphan solo I'm guessing you'd need a mix of both. Victories posted here sound like they cut it pretty close with the clock, I'd wager at least one or two Kyogre is a mandatory minimum for their higher DPS. Higher TDO is great for finishing the fight but you need to make sure you've given yourself enough time to do so.
Yep. That’s the team I used and it was rainy. Revived the two sceptiles and the gyarados and finished it with the Kyogre right where it sits. I can’t explain it but that’s what happened. Dodged well.
Failed first time through with a L30 HP vapor instead of one of the Sceptile.
As I said, I can’t explain it but it happened. I’ve soloed Machamp with some really weak seeming teams before, too. Gotta dodge well sometimes and get lucky with the boss charge moves being infrequent.