As the Original Poster and for safety reasons I feel obligated to add this
I don't know what (1 post) krislou80 was getting at, short of advertising his website/product "Mr. Gasket Shackle Kit". However, I would never advise anyone use an automotive size shackle for an RV which generally has to resist much much heavier loads and forces. Stick with any name brand system built for RVs and you'll be safe.
BTW.....would you by shackles from a company who's ad for their own product calls it "inferior"?
"Choosing the right shackle can be difficult because of the seemingly endless choices in the market. So you'd better make sure you won't end up with a unit that's not as inferior as the Mr Gasket shackle kit."
2004 Dodge Ram 5.9L Cummins HO, Auto QC 4WD SRW LWB....2004 HitchHiker II LS, 30.5 RLBG, Dbl Slide....2005 Sandpiper Sport 19ft T21 toyhauler