I kind of like the roll ups, personally. Here's a photo of the old sliding doors, as well as a shot from behind so you can see how they were done. It looks to me like Oliver just used a standard 2-channel sliding door track fastened to the back, and so the 'frame' was just to cover the edges.
Airstream do a sliding door with an aluminum extrusion frame. If you can find the right extrusion, then I think it would be a really good look in an Ollie. Eagle Aluminum is a good source for that sort of trim -
Another style for the older Ollies was just a simple cabinet door, similar to a Casita. That might be the easiest thing to retrofit, since you could size the door to cover any holes that are leftover from the roll ups -
Here are some Casita shots to see what they do. The painted version looks best, imo -
Earthcruiser has done the same, but with a more modern look and sturdier hardware, and since their interiors are so similar, I don't think it would look bad at all an Ollie -
They also do what looks to me like a routed sheet of HDPE or maybe PVC, with a frame that looks like it might be the same. I really like the hardware in this video. You can also go back in the video and it looks like on one door, they've cut a sheet or assembled some aluminum extrusion for the frame -