I found the below tag in the CoreGoodieHuts.xml.  It looks interesting for modders so I thought I would share it.  It appears give the ability for lairs to increase in challenge over time as the PCs gain levels.  I haven't tested it yet though.

    <GoodieHutType InternalName="Lair_TrollShaman">
        <Name>Shaman's Hut</Name>
        <Description>From the simple shack's chimney, smoke rises. Smoke of a brilliant, unearthly blue... the smoke of a channeler's fire.. Potions of some sort are being brewed.</Description>
        <Rarity>-1</Rarity>
        <AutoDestroyWhenNoGuardians>1</AutoDestroyWhenNoGuardians>
        <LikelihoodOfTreasureDropWhenAutoDestroyed>100</LikelihoodOfTreasureDropWhenAutoDestroyed>
        <BarredTerrain>River</BarredTerrain>
        <PreferredTerrain>Forest</PreferredTerrain>
        <PreferredTerrain>SwampTerrain</PreferredTerrain>
        <ReleaseGuardiansOnInfluenceHit>1</ReleaseGuardiansOnInfluenceHit>
        <SpawnRating>0</SpawnRating>
        <UpgradesToGoodieHut>Lair_TrollShaman_Final</UpgradesToGoodieHut>
        <UpgradesToGoodieHutInTurns>360</UpgradesToGoodieHutInTurns>
        <TileDesign>L_Troll_Shaman_01</TileDesign>
        <TileDesignForTerrain>SwampTerrain:L_Troll_Shaman_Asag_01</TileDesignForTerrain>
        <DrawnIcon>Lair_Troll.png</DrawnIcon>
        <IconSize>50</IconSize>
        <OnSelectSFX>Click_Troll_Camp</OnSelectSFX>
        <Medallions InternalName="">
            <All>L_Troll_Shaman_01.png</All>
        </Medallions>