DO-328 and jet derivative are great aircraft, but I am fairly sure that the doors are integral to hull integrity in flight. The DO-228 however (non-pressurized) version that preceeded the later models would most likely be a better jumping platform, if you could find one with interest, also has a double door in the rear which would make for good exits. As long as we are just pontificating and throwing out ideas.
Flea, I am reading, but you and I both know there are more than just one or two issues to resolve for some specialty aircraft to arrive.