I was testing a mod that required the editing of my savegame files, so I followed the guide posted here to extract and modify my savegame using vfstool. However, when I attempted to repack the edited files I noticed that my savegame file size jumped from 292kb to 7144kb. Something was wrong. I had followed the readme instructions exactly and used the 'sin' command to repack the files but for some reason the program was not compressing them properly. I used the following commands:

mkdir save
vfstool e save.vfs save (3 files extracted)
(edit over)
vfstool sin save.vfs save (3 files imported)
vfstool md5 save.vfs

I cannot figure out what might be the problem. I tried extracting the files from a fresh savegame and importing them straight back in unaltered and the same thing happened, so I am reasonably confident that my alterations are not the cause of the problem. Is there some vital step I might have overlooked or is there another way to edit my savegames that does not use vfstools?

1) you did nothing wrong
2) there is no other way to edit saves
3) sometimes the filesize will jump, don't worry about it too much, the save should still work ingame

(ps: loading the save and saving it to a new name will probably solve your filesize)