I've seen a bus owner use rope glued over the gap you're looking to cover.
Don't know if that goes with your interior motif, but it might be a lower cost option if you think it will work?
1/4 round comes in many widths and is bendable. The rope idea works well also as there are any types and size of rope you can use. Bendable and make 90* turns around corners, glued or tacked with brads.