Autosave works just fine, basically, so all you have to do to make sure you don't lose your work, is this:
1) Set autosave to go off every one minute.
2) When you finish working on your map, instead of saving, wait one minute (to ensure autosave is up-to-date), then go to Open.
3) Click autosave.map once, then press CTRL+C and CTRL+V. This should make a copy of the file named 'autosave - Copy.map'.
4) Rename 'autosave - Copy.map' to your desired filename.
Not quite as speedy or eloquent as File -> Save As, but it works just fine.
Now, you may ask, "What about the next time I want to save it?". Just do the same again, only before renaming 'autosave - Copy.map', append something like 'old' or 'backup' onto the older copy's filename for two reasons - 1) to let you rename your map file again, and 2) because smart people always keep backups anyway.
It ain't perfect, but your only other option is rolling with Gtk1.5.0, and I understand that for some odd reason everyone's unwilling to do that even though it's the exact same editor....