I start withto get some lifesteal

I getbecause to balance the damage you get from

rapid bite with the attack speed you get from these boots

After you get boots its great to havebecause this

makes your character better to chase, and survive.

After you get that frozen mallet you getyou have the

combo if great damage from your must important spell rapid bite, great attack speed, Much health and great chaser allready

:D, but, now we have to balance it since you have more attack speed then damage, so its time to get:
since life steal and alot damage :D

But later game, you can see they have gotten alot armor even if they dont buy armor items, since they get armor each time

they level up, so its time to remove some armor, so its time to get
for removing 45 armor and alot attack speed and damage.

Later, you need some armor and magic resist and that revive has allways helped someone so get
wll help you alot, since the health from frozen

mallet and armor/magic resist from guardion angel, will make you alot harder to kill

I takeGreater Seal of Resilience (armor) for more armor to balance the health you get from frozen mallet.

I takeGreater Glyph of Warding (magic resist)

All the champion start with 10-20 armor, soGreater Mark of Desolation (attack penetriation) will make it easier to get first blood.

In the end we haveGreater Quintessence of Alacrity to balance the damage from your rapid bite.

If you have no ip, or not enough to get all the runes at the same time, then follow this order:

1st attack penetriation
2nd attack speed
3rd Magic resist/Armor

sry for having the low info, but i hope this will help you play trundle and hope this is enough info or the rest info you're able to find out ourself ;) Good luck.
Please comment what you liked or what you didnt like :)