I agree with everyone, the K member jacking point is good, but I too have noticed mines starting to get dented up cause my floor jack has those little tabs on the nose that seem to bend the metal. Also I have noticed my jack stands bend are denting the frame rails too. I have always place the stands at exactly the same spots and the frame rails have corresponding dents in them.
I think the 2x4 idea is good...just be careful, wood can be slippery.