I had the same problem getting SP for my gladiator. So far, I've been able to do ok at the tougher camp. Since about rank 12, I've been taking all my leves at the 20 camps and attempting them with my gladiator. If I can pull it off, it works pretty well for SP, but if I'm too weak, I'll switch to my higher ranking CON to finish it. At first, I was only able to do one or two, but I've worked my rank up to 17 GLD now and can do most of them without having to switch.
If you don't have a higher ranking class, I would recommend learning which leves are the easier ones for the 20 camps and just signing up for those. Its a pain, but use your guardian on those and you'll eventually get past that terrible in-between spot you're at.