You could try a weighted blanket at night (http://www.kozieclothes.com/sensory/weighted-blankets). My son used to have proprioceptive (among other sensory) issues, so we had him wearing weighted belts, compression vests, etc. and the calming effects of these items was remarkable. You could consult an occupational therapist for the proper weight for the blanket for your son's size. You can make your own using those plastic pellets people use to add weight to stuffed animals and bean bags. There are several tutorials online.
The pressure on the body can have a calming effect, which is why he may need it to fall asleep at night. That could also explain why the seatbelts and the pressure of being strapped in his carseat helps him to fall asleep too. It might help to pour Epsom salts in his bath before bed, as that can be calming to the central nervous system. It may or may not work, but could be worth a shot.
Other options might be joint compressions where you push the joints together. Here's a great site for video demonstrations: http://sensoryandmore.com/2011/08/11/joint-compressions/ I also recommend the brushing technique as well that is mentioned. We purchased the same brush that the lady in the video is using from the therapy place my son attended.
Best to you and your son!
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