Do regular DLs as best you can and use straps if you must, but do those farmer's walks as well to help with forearm strength.
Even if you can only do like 3 reps on the .5 CoC, that's probably okay. Low volume, heavy/high resistance is great for building strength. I want to say that mine is 100lb of force to close, and like I said, I can generally do 6-8 sets of ~15 reps. I actually use chalk or hold the bar with paper towels in my hands for extra grip, and I've had no problems with weights that you're doing. Sometimes I'll need to loosen and regrip mid set when my hands start getting moist.