I know this might be a little late at this point...but I just use a foodsaver vacuum sealer and it seems to work well. One guy I know saves his meat packing trays throughout the year, and apparently that works well to place the herring on, before vacuum sealing. The other idea I had is to first brine the herring, and put them into a ziplock bag, brine and all, making sure there is no air left, then freezing them. Some of the commercial guys do this with their fish and prawns, and it seems to work quite well. Just a couple thoughts...
-Dan