I came across this in another forum. http://www.watto.org/extract/download.html
They have a game file extractor that will extract files out of RB3D's vol files. It is an easy Window interface, one click and extract (okay, maybe a few clicks) type of program.
The VOL files I tested it out on worked nicely and easily.
The program is free.
The full version ($5) is designed to make/put back together the game files, but RB3D's Vol files are not currently supported.
But for extraction, it currently supports over 1,300 games.
EDIT: Have done some additional testing, with modified vol files like PL1, it says it can't open the files, but if you select the "Use a Script" option, it has no problems.