Yes, the bags work. I used to make them for S7 punches. There are two types of foil they normally sell. For S7 and other grades like A2 or D2, I'd recommend the 0.002"-0.003" thick stuff. Thicker will work and goes to higher temperatures, but it's a witch to fold. The negative to this is that the thin stuff will develop pin holes more easily.
My old method for making bags is as follows (note the stuff should come on a roll...and is fairly expensive):
1) Roll out the foil. Measure out the length of your part and then add 4"-6" to it. Make a mark with a Sharpie marker (or your finger...the grease will show up).
2) Use metal scissors to cut the width at this point.
3) Take the cut sheet and fold it in half longways (so you would have a piece that is as wide as the roll and as tall as your part + 2")
4) Using your part as a gage, mark a line from the edge of your foil that is about 3"-5" wider than your part (this grows as part shape/size/complexity grows). Again, make a mark and cut.
5) Now you'll need a straight edge and a roller, preferably one with a heavier metal end. The bottom of the bag where the fold is should be facing you. You should have a cut edge to the right, left, and open at the top. Take the right edge and extend it over the side of a table...eyeball it for a 1/4" or so. Put the straight edge inline with the table and fold the foil up over the straight edge.
6) Get your straight out of the way and press the fold down with your fingers. Once complete, tap the fold in a few places with the small roller to set the fold. Then roll up and down the fold line with the roller until it's flat.
7) You want to repeat step 6 until you have a minimum of (3) folds, then do the same to the left side.
8) After your folds are in, use something like a broomstick handle to open up the top end of the bag. Slide your parts in until they're maybe 1" or so from the bottom. Using a metal crimper, once the part is in place you'll crimp the bottom 3/4" below the part.
9) Now seal the top just like you sealed the sides. 3 folds are a minimum. Don't try and get your folds all the way to the top of the part. You'd like at least 1" of gap. Also, the heavier roller helps here to beat the folds down. If you don't have that, the crimper will help you develop arm strength.
10) Now take your bag and extend the bottom 1" of open space over the edge of the table. Fold up towards you. Fold the top over in the opposite direction. It will look like a "boxy" letter S. You now have a bag that will stand upright in your furnace, but 1" or so away from the elements on the walls. As your parts sound thin, this vertical method will give you a much better heat through than setting them on the ceramic hearth plate (which acts like a heat sink).
11) Visually check your exposed bag areas for pin holes. if you see one, cut your bag open, pull the part out, and do it again.
12) When you heat treat these, make sure you get them quenched quickly. Check your hardness out of heat. If you're not at the peak out of heat hardness on these, drop down on your tempering temperatures. It's better to temper the stuff a few times than drop it under as I've never had much luck re-heating S7 to peak hardness. I always seemed to end up 1-2 points off the second time around.
If you're new to this, get some surgical anti-cut latex gloves. They're thin so you won't lose dexterity. When I learned, I didn't use gloves. I did manage to cut each finger at least twice in the first week. This stuff is like a pliable razor blade. Luckily, with experience, you learn how to do it extremely quickly w/o gloves.
If you do try it barehanded, you'll note the cuts are like nasty papercuts (they also dry out quickly and like to crack). At night, before you go to bed, goop up the cut areas with vaseline/neosporin and throw socks over your hands to keep the goop off of your sheets. That'll help 'em heal nice and quick.
