The boots needs to be an item that you might need to change due to dealing with DPS or magic champions. If you think you are going to have a problem with the magic champions then get the Merc Treads, if you are dealing with DPS champions get Ninja Tabi. The other items are set in stone, just got to know how to use trundle consider his not a lone champion unless its a magic champion that can suppress you during a fight. Trundle does some major hits on magic and squishy champions no matter what. Even when he gets his phantom dancers then he starts doing major damage to the tanks even. Very awesome slow bite and ult kills. All used in a good set up combo.

The reason I got these set up on the runes is due to needing attack speed onto of the armor pen. By the time you get phantom dancer you should have 60 armor pen and attack speed over 1.4. I probably update this if I can find a better combo of runes for the champion but right now this is the best work out for Trundle.

The best way to get your kills is to lane with someone who has a slow or snare/suppress. This will give you a 90% kill rate during fights with you and your support champion at your side. If you solo a champion fight you might need to play it safe but most of the time champions will be running away because Trundle bite and slow are a killer combo on squishy champions because of the damage being dealt during the timed right bite you will bite then hit right away.

Good Lanning Partner Champions:

Sion
Janna
Ryze
Xin Zhao
Rammus

this list is very general because you get the idea the stun is more fun or a snare. But slowing champions can really make it too. He can slow even more and do major dps before the champion has a chance to get back.

Pros:

Fast Killer *First Blood*
Awesome dps damage during team fights
Makes running nearly impossible of done right
Late game = Back dooring if needed

Cons:

Target for snares and disable abilities
Target because of health which has more then most tanks
Just in all a general target if played correctly

Early game, play it safe till level three and then with your snare/stun/slow champion set up a gank get them build in far enough to your side and when ready and with good health go take one out. If there are two on the lane one will try to help the other but the other might run which is ok get the first kill.

Mid game Trundle should have his first tower on his lane which allows him to finally move around. So try to get a blue buff and this is where the fun begins. Go after any squishy champion they will not be able to run very fast due to trundles pillar of filth.

Late game Trundle should be taking enough armor away to where tanks will be feeling him hitting them. His slow as well will help them team kill those tanks and squashies from running like wussies.

This is a very basic idea and it will depend on how well you play him. I have owned him since he first came out and I just now really am understanding why armor pen is good on him,