Wheelchair van for James Lucas

My son James Lucas Jones is an 11 year old boy who has brain damage from open heart surgery in 2011, which has caused him to suffer from a severe movement disorder. He suffers from cerebral palsy, he is non-verbal, and has severe challenges eating, toileting, and sitting without maximum support/assistance. Although he faces challenges every moment, he is the bravest and strongest boy ever.  
Transporting him has become extremely difficult and painful for him because of his height and lack of trunch support. We have a small car and he barely fits in an adapted car seat. He is getting too heavy to pick up and put in a car seat, and it is  becoming very dangerous, as he is almost as tall as an adult.  Also breaking down and putting together the wheelchair in the rain, cold, heat and in parking lots has become very difficult.  He needs to be able to get in the wheelchair in the house using a lift, and then roll into a van, this would be life changing for us.  We want to take him more places but are very limited.  Any considerations would be greatly appreciated.