I don't sew and I don't like the harvest procedure for the 'bag system'.
2 key considerations:
the bag support system must handle 'full weight'-
and the bag can not stretch.
check Bentley's info-
http://www.redwormcomposting.com/category/worm-inn/

Yes, I've watched his interesting videos when he loaded it up with food scraps several times. I've been running a 55gal plastic flow thru barrel that I built (not lately cause I moved recently). I added a lot of food to that too and the worms handled it fine. I'm wondering if the breathable walls make that much of a difference. I can see how weight would be an issue and harvesting tedious. Maybe for an experiment I could take a nylon sack and start filling it up to see what happens.

The difference I've found so far verses a bin is you keep adding water instead of having to worry it's too wet and draining or adding bedding to soak it up. Much easier to for me to add what I need instead of having to remove what gets in there.

Found with bins no matter what I tried the vents always clogged up and no longer worked after a few months and ended up with me keeping the top off.

Haven't harvested yet from the Inn, but can't see a problem with dragging out the bottom... not compaired to bins :P. Probably end up doing a digging/massage combo to get it flowing.

I use a Coleman high stand to hang it, good up to 100lbs
http://www.amazon.com/Coleman-Stand-Burner-Stoves-Cooler/dp/B0009PUPUG

In building your own, assuming it large you better work out a system to attach the bag to the stand. If it's not reinforced any hook will just pull through the material.

To estimate the weight of one's vermicompost 7-8 pounds per gallon might be about right.

Are you sure about that? That's the weight of water. I guess if it compacts by settling and is pretty moist. Come to think of it, the stuff is pretty darn dense if compacted. I had less than 2 feet of finished compost in my barrel at one point and it probably weighted 200#, that's just a guess. It was too heavy to transport when it was time to move. It was a sad day when I had to empty the thing out.

This is a very good instruction on building a bag system:
http://www.instructables.com/id/Worm-bin-bag-for-indoor-vermicomposting-and-easy-s/

Here is one bag system that I recently made, with a detail of the pros and cons and what I learned. I hope that you will find my experience helpful as you design and build your own system.

Good luck with your new system, and let us know how it goes!

http://forums.gardenweb.com/forums/load/verm/msg0102493810514.html