It would be really nice if the-powers-that-be would recognize that there are these types of books that fall into a genre called "Fiction" and that series name/# (in addition to sub-title) is actually a thing...
I know those aren't supported under DC for ePub2, but I think there are some possibilities under ePub3...at least from what I've heard. In the meantime I've been using the Calibre metadata tags for series/# and using the colon space for subtitle. Any book reader worth their spit would read the Calibre metadata....
General Failures 3: The Wreckoning - Bob's Revenge
would be:
<dc:title>The Wreckoning: Bob's Revenge</dc:title>
<meta content="General Failures" name="calibre:series" />
<meta content="3" name="calibre:series_index" />
If a standard metadata becomes available in the future for epub2 then it would be the easiest thing to regex the calibre metadata into the proper format.