I have chosen Some different rune and masteries setup on the two builds I have with trundle, that I will come till in the Builds.
Both build also have Exhaust and Ignite because both build shall have capacity to 1v1 agaisnt most champions. Trundle with his rapid bite and the summoner spells are a excellent first blooder. Use it to your advantage.

BUILD 1
Build one, the damage build, I have chosen Greater Mark of Critical Chance just because I get crit pretty late in the build. And crit is really nice on Trundle, as it synergizes well with rapid Bite in early stages of the game., but there is other items then crit items that are better to get early on. Also got Greater Glyph of Scaling Mana Regeneration, for staying power in lane.
Together with his passive, Vampiric Scepter and those runes, he should be able to stay
in lane a long time.
I rely on in this build that I get some assist and kills with Sword of the Occult, as 20 stack abilitie, the movement speed is real good on trundle., and get the other real damage items later in the build. I you dont like Snowball items i recommend a B.F sword there instead, and finish Infinity Edge after Zeke's Harbinger
The Frozen Mallet i take before Starks's fervor, because it gives me the chance to chase down junglers.
But when u get Zeke's Harbinger, u notice how well it synergize with trundle, and all of sudden, your threat against AD champs and tanks skyrise.
After this I prefer Bloodthirster, because I feel that lifesteal is essential on Trundle.
The last item I have is the Phantom Dancer, just because it helps me chase down mages a lot easier. Bur if u meet alot of High HP champs, exhange it for Madred's Bloodrazor, as it actually synergizes better Trundle. But the Phantom Dancer i think synergize better with his lifesteal.

BUILD 2
I usally don´t use this build as much as the other build, but when u meet a whole team off cc freaks, it is almost neccessry with off-tanking. And can be viable if u feel that your team consist of alot of squshies and need someone other then the tank with some staying power. Thats why I have A different Mastery tree and some Runes. Alot less harassing in early lane phase, but opted to take some punishment and let your other damage dealer to do some damage.

Ive included Frozen mallet And Stark's Fervor again, as they always are good on trundle.
As I usually do with damage dealers that need protection, i often include Hexdrinker and Atmas Impaler (especially as I have lots of health with Frozen Mallet]].
The Banshee's Veil is really great on trundle late game, but if u feel u dont need it, and need some more damage, and/or Armour, Madred's Bloodrazor is real good substitute, as u havent stacked so many other high damage together.
Ofc, If meet a AD team and play with this build, Ninja Tabi is really much better. Against Melee Champs, Your Contaminate Zone is a much more viable fighting area, and the cc reduction on it almost negates Mercur'y Threads viability