This is a guide to be able to make a decent jungler, tank, damage output and support. Yes that's right, LIKE A BAWS.

Greater Mark of Desolation
Armor penetration is a good boost for trundle early game giving you just enough damage output to gank decently. As he has a Pillar of Filth to slow the target he and the laning team have enough time to burst down one enemy champion.

Greater Seal of Resilience
Some armor to defend himself from the minions. Reducing the damage minions in the jungle do to him might seem unneeded, but if you count all the damage reduction from all the incoming minion hit it is a decent number.

Greater Glyph of Focus
Cooldown reduction is very usefull since Trundle gets his lifesteal mostly from his Rabid Bite ability and the buff given by the Rabid Bite.

Greater Quintessence of Evasion
Why do I use dodge? Because I can, LIKE A BAWS

You start with a Vampiric Sceptre, not the usual armor + 5 health pots. This is because Trundle has enough damage output and lifesteal with this item to stay alive and bring down the blue buff in the start. I do recommend a pull from mid or bot though. With the pull you will have about 75% of your hp remaining after you killed the blue buff.

Your jungle route is as follows:

Blue buff -> The wolves -> The wraiths -> Red buff -> Golems.

After these jungles you will have enough time to gank top lane, this is what I recommend you to do, unless your team is pushing you want to continue jungling.
If there is no enemy jungle, you can go for the enemies blue buff, if not you go back to the wraiths and after the wraiths you can gank mid. If it is not possible to gank mid you move on to the wolves. After you've done the wolves you attempt to gank bot. If this is, once again, not possible you go back to the northern part of the jungle and just kill the minions that have respawned, and try to get as much ganking going on as possible.

The items give jungle a decent amount of health and damage done. I did not buy too much attack speed intentionnaly. The Contaminate spell will give you more than enough attack speed combined with the Trinity Force.
Also these items make Trundle intensively usefull late game. Not only are you able to make a decent tank and do enough damage output, you can also support your team by placing the Pillar of Filth cleverly to save a dieing teammate.

I chose these summoner spells because of multiple reasons. Smite is usefull for your jungle. The ghost is chosen because of the speed it provides. If you need to gank an enemy lane you'd better come out of the brush sprinting to get close in a small time.
Also the Ghost spell makes you less vulnerable. Imagine you walk in a brush with the entire enemy team stacked up. You immediatly place Pillar of Filth between you and the enemy team and you activate Contaminate and ghost and you springt away. This way you make it out alive.

The masteries are chosen according to minion damage reduction. With these masteries the damage produced by the jungle minions is severly reduced and even if you do not have runes you will still be able to jungle with no problem at all.
Also I chose some cooldown reduction to increase the damage output produced by your Rabid Bite.

If you have any questions add
Beeldscherm - EU-West
Fatty Willie - Eu-West