What I did when I started heriocs, using a pali tank, was to gear em up with daunting handguard, daunting legplates and the rest was tempered saronite gear.

You need 535 def to avoid crits but if yer a lil under its not that big of a deal

With herioc UK first boss all yeh really gotta do is make sure all yer guys can cast on each other put em in a semi circle and have em use /target frost tomb in there dps macro. If yeh use melee use the interact button the whole time with /target frost tomb makes it really easy. If yeh have a pali use the shadow resist aura helps with those shadowbolts.