I'm afraid to get the answer to this question......
With the halfgiant skin, Gunther has a 20 constitution. He just leveled to 24, giving an ability point.
I place that in Con, making his constitution 21, hence fitting the requirement for epic damage reduction.
However it doesnt show up in the list of available feats.
Without the giant skin, his constitution is 15 (I think), 16 with the level jump to 24th level.
The game only factors off the base number (no skin taken into account)? So epic damage reduction cant be taken unless Gunther's base number somehow jumps to 21?