I use something from my blackpowder handgun shooting days.

Crisco.

You useit to prevent chain firing in a BP handgun, and it also keeps the barrel lubed for the following shot.

Very small amount goes a long way, last a whiles and is oderless also. Also costs like $2 for a 2lb container. Just keep it in a leak proof small container like a 35mm film roll container.

Been using it for over a year and got hundreds of shots. String still looks like new.