Ok I just did a crane course, and a boilermaker and in younger years did a lot of rock sports, so have a good understanding of how metals can be affected, if your such a tight wad not to spend $20 or so to by rated shackle maybe you should sell your camper/caravan and sit at home twiddling your thumbs to watch your money do nothing, otherwise I hope you trailer stays behind you when I drive past you.
I also am bashing my head against a brick wall to convince my inlaws to replace their $2 shackles on their 3.5t caravan which have been on it for 8+years, and they just had it passed by the RMS NSW as is
Cheers
Jason