Hi all,
I am "Trundle BEAST", a NA Trundle OTP since season 11, currently ranked Gold 1.
I play league since season 3, and have mained Evelynn in season 3 and 4, then Warwick until season 11. I have been Platinum since season 4, on OCE, EUW, and NA servers. I aim to reach Diamond in season 12.

I like to think a lot about my runes and items, rather than just copying what other players do.

After many games, (about 500 ranked this season), this is the runes/items I came up with. I am ranked #2891 world and #311 Trundle NA on leagueofgraph, among the top 1.7% Trundle players, and climbing.

I completely understand why the common build is tank boots, divine sunderer, tank, with PTA keystone. However, IMO, trinity is better. It does (much) more damage to squishy targets, turrets, and clear monster/cs faster. + the mythic passive is much better. And now sheen works with Sterak base damage boost.

My build scales much better. You become a late game beast. You get enough resistances when ulting enemy tank anyway, when you need resistances. You're still very tanky without your ult. Sterak + GA makes you a great frontline.

I won so many games with backdoor. Full build you can destroy 2 nexus turrets without minions. Trinity + titanic + sterak + hullbreaker = kill a turret/inhib/nexus in 2 seconds, literally.

When RIOT makes buff, sometime you see +3 AD, or + 10 base dmg on an ability. You might think this won't change anything... but it actually allows to clear faster. If you clear camps faster, you get gold and experience faster, and move around faster. This is huge.
Similarly, a build that does more DPS and gives more mobility will have this effect, you'll clear camp faster, gain gold/exp faster, have more opportunities to gank or do an objective.
This is why lucidity boots are strong. Also, if you kill you enemy faster, you don't need to tank his damage. Trinity Force gives you AS, AD, AH, MS. Titanic gives you AOE damage on aa, scaling great with trinity AS and W AS.
When I check my stats on https://www.leagueofgraphs.com/summoner/champions/trundle/na/Trundle+BEAST#farmingData I am usually in the top 1% of Trundle jungle cs.

I usually start botside for a faster leash from botlane, then fullclear bot, then take buff from topside, and then either gank top/mid or invade jungler, then take scuttle, finish top clear, first back.

Ward enemy jungler, keep track of where he is. Clear you jungle, gank when opportunity, do drake/rift as soon as they spawn. You should know where enemy jungler is and if you have prio. You're Trundle, you can 1v1 anybody early. Often, if enemy jungler killed scuttle, use plant to jump in drake/rift pit, put your control ward, sneak drake/rift. They think they would've seen you coming because of scuttle vision, but you sneaked with a plant.

If ahead or equal, group with your team. In teamfights, you have to go in and out, you're tanky and do great DPS and CC with E, but you want to stay alive as long as possible, your passive will heal you TONS in long teamfights, and you're OP with conqueror + trinity + q stacked. Staying alive for a long time in teamfight makes you have a huge effective HP pool, because you regen so much.

If your team is inting, ignore your team, and split-push. with titanic, trinity, sterak, hullbreaker, and smite, you clear waves instantly and kill turrets in 2 seconds. Actually, when you see a drake or baron up in 30 seconds, you know enemy team will group there. DESTROY OPOSITE SIDE LANE. You can backdoor in seconds. If enemy top is waiting for you, kill him. You're a duel beast with that build, you can 1v1 dueler under their turret. You have challenging smite, sterak, trinity, GA...

Trundle is naturally a strong split-pusher, as he can aa-reset with q on turrets, and has AS boost with W. Also, he is a strong dueler, so he can 1v1, and then kill turrets.
Why not enhancing this? Trinity force procs on turret, it does much more turret damage than DS. Titanic also proc on turrets, and allow you to clear waves in seconds. Hullbreaker boost this damage further, and enhance your 1v1 potential.
With 2 items, you can splitpush and backdoor very efficiently.
With sterak and hullbreaker on top, and you can 1v2 enemy team under their turret + destroy 3 turrets, inhib and nexus in 1 minute.
With GA... you can do this https://www.youtube.com/watch?v=adv_5S26eys&ab_channel=Tundra_Hunter