You need to find a local fabricator who can install a 12volt actuator. It needs to be mounted to the door frame and door and the lock assembly removed. The actuator would open or close the door and then hold it shut during travel. It could be operated on the outside with a key to energize.
If you look around your area, you'll find companies that are making custom trucks and van conversions. Almost every repair truck or specialty companies like DirecTV etc, use fabricators to outfit their vehicles. Installing an actuator is a pretty simple job. SOmeone who is really good should be able to incorporate the wheelchair lift function with the door opening.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab