I used the “Ruby Red” jaw strap to train myself to sleep with my mouth shut like this from my CPAP supplier. Legend Medical-Ruby Adjustable Chin Strap, Fits 3 Sizes Small Thru Large https://www.amazon.com/dp/B00BV8Y6YG/ref=cm_sw_r_cp_api_i_7JcdFbZQNP0BC
Also got a little rubber band and made a tiny pony tail to put beneath my mask’s head/neck band. This helps the gear not slide off easily.