I suggest a threadlocker like blue (removable) Loctite or similar brand on all rack bolts.
On a couple tours, I saw a couple people that lost a rack bolt from vibration.
On another tour we were over 100 km from any form of retail and met one biker that had already run out of spare bolts for his and his wife's bikes, he wrapped tape around his rack bolts so that they could not unscrew far enough to fall out.
Last time I bought any, this is what I got.
https://www.truevalue.com/6-ml-remov...hread-locker-1