You already know and are experienced with your Bubblebro. Consider using him. Bubblebros can do Trials just fine.
2.0 Titan here, and I swear by Defender in Crucible. Probably the biggest mistake Defenders make is playing like Strikers. If you're going to play like a Striker, switch to Striker (and I do; I play about 50/50).
If you're going to play Defender, take up a support role. For me, I like to use a low RoF/high impact pulse rifle (Super Pox VLO with Perfect Balance, Messenger with Perfect Balance, and Hopscotch Pilgrim with Braced Frame all get my top votes). Try to stay mostly at mid-range, and support your teammates' fire. Snipers and Thorn are your primary targets. You want to try and two-burst them. If you're using one of those PRs I mentioned, you can two-burst clear out to sniper range (I'm talking across Pantheon sniper range, not across First Light sniper range), so use that to your advantage.
Use suppression grenade, and do NOT use an armor piece that increases grenade throw distance. You'll mainly use the grenade like a Striker's flashbang or Hunter's incendiary, but your primary usage will be keeping it in reserve when you expect a super is coming up. Someone on the other team activates Arc Blade, Golden Gun, or Radiance, try and get a tab on where they're coming from, and throw your suppression grenade so it lands on the ground near their expected approach. This is where not increasing throw distance comes in handy. You want it to land where you aimed it and stay at or near there, not ricochet off somewhere else from the extra velocity. If you did it right, congrats. You just cancelled their super mid-push, and now they're fucked.
Also, decide beforehand how you're going to be using your bubble.
As cool as 3 sounds, and as great as it is in regular Crucible, I'd recommend against it in Trials. It usually doesn't go as well as you planned. Armor and Blessing are generally much better.
Finally, back up your pulse rifle with your choice of:
I would NOT pair a sniper with the pulse rifles. That gives you long range and longer range, and leaves you weak up close. If you want to snipe, use something that's great at close range like The Last Word as your primary.
Also, if you run shotgun, master the art of crouching at corners you expect an enemy to come around, especially if your teammates are nearby. Position yourself a bit forward of them and lay your trap. Oftentimes someone will expect only the obvious radar blips, come barreling around a corner to attack your teammates, when BOOM. Plays well to a defensive player whose aim with their primary just isn't great.
As far as general play... be cautious, know the map, and watch your radar like a hawk. Use a Third Eye primary like The Messenger if possible. If you know where your enemy is, step out from cover, fire a burst, step back, step back out again and fire another burst. The great thing about pulse rifles is they deliver all their firepower all at once, so this is far more viable than doing it with one of the other three primaries, and goes well with a defensive style.
Fight like the Red Baron. He didn't stay alive as long as he did because he was the best. He stayed alive because he knew how to pick his fights and felt no dishonor in running from a fight he knew he couldn't win. If you're facing a bad situation, don't feel a need to be ballsy and attack. Fall back and see if you can get the enemy to spread out and give chase.