If theme is important to you look elsewhere. I couldn't come up with a theme based deck that had a fighting chance against this scenario.

After playing The Lonely Mountain several times I determined card draw and dealing with treacheries were the keys to beating the scenario. Card draw helps with Bilbo's burgle attempts and the treacheries can just be brutal and game ending. And even if you have both of those bases covered Smaug can wipe you out pretty quick. In fact, when you get to questing stage 3B players player 1 will want 3 chump blockers standing by.

I'd recommend not questing successfully on Turn 2 (Turn 1 is kind of a free turn for players with no quest phase). Instead, continue to get key allies and attachments on the board.

Why Thalin? There are 3 bats in the encounter deck that he can one shot by just questing and the breathing space it provides when that happens is hugely beneficial. And, with Dáin Ironfoot in the other deck, Thalin quests at a respectable 2.

Bifur allows players to get those 2 cost lore allies on the board all by himself and will always be in quest mode.

Gimli will be the hammer when it comes to dealing damage to Smaug. You'll want some combination of damage on Gimli, Khazâd! Khazâd!, Unseen Strike, and Dwarven Axe when making your attack(s) on Smaug.

Shadow of the Past can come in very handy so if it's in your hand pay very close attention to that top encounter card. If you can get a non-burgle encounter card on top of the deck when Smaug draws his shadow card it can make all the difference.