The sides are the most difficult to seal because of the need to maintain a clearance for the door to slide in its track. Various types of seals are offered to deal with this type of door. People keep inventing better types of seals, so make a search to find the best that are currently available. If the door is installed inside a jamb, you may be able to install brush seals on the outside of the door to contact the jamb. This method creates significant resistance, so limit it to doors that have motorized
operators. You can reduce the resistance by arranging a brush seal on the door to mate with a “knife edge” installed on the jamb, or vice versa.