Exercises to help with a tight trap

Some background: I've worked for 5 summers in the canadian tree planting industry, planting ~4500 trees a day. The wight and movement patterns are very imbalanced and as a result I have built up a lot of muscle imbalances.

In particular, my left trap is very tight and so my left shoulder sits noticeably higher than my right shoulder. I don't have access to a gym, but I have been doing calisthenics based workouts at home with the addition of a weight vest and various resistance bands. For my shoulder, I have been focusing on strengthening my middle and lower trap to help relieve tension from the upper portion. I have also been doing trap raises with resistance bands under my feet, focusing primarily on a slow and controlled eccentric movement and lengthening the muscle under tension.

I have definitely seen a reduction in imbalance and reduced tension, but am wondering what other exercise/movements/stretches might be useful.

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