Recently I've been adding stans sealant to tubes that have slow leaks, particularly my fat bike which was frustrating me to no end. Slow leak with no detected hole. Sealed right away. Our local problem is blackberry thorns which leave pin prick holes that are hard to find.
Tubeless would do the same but I am still not there for a touring bike as a flat would be problematic in the field. You need to pack extra sealant, a large hole repair kit and an extra tube if you can't get the tire to seat with a hand pump. In that regard, stans sealant in the tube is the next best compromise.