I would store them in a cool dry place get a air tight contaner. I really dont know as I buy mine the day or day befor I use it. but I would say best to keep away from moisture/humidity so a air tight container will do
I buy my LDME in 20kg bags and once I open it I put the lot into 5ltr plastic tubs, they're not air tight but I haven't had any issues with the stuff going stale. A bag usually lasts me 6 months, maybe a bit less