Freezing yeast question

I ordered some glycerol... (also need some for my cigar humidor)

I'm going to be doing a batch using some Thames II yeast (in an 1850 porter soon) I'm going to try yeast washing and freezing the yeast culture for the first time with this batch.

How much glycerol to washed yeast I've read numbers from 15% of washed yeast volume to as High as 50% ( http://www.danstaryeast.com/library/using-glycerine-freeze-yeast ). Only have access to my small no-frost freezer.

I've read if using a no-frost freezer to insulate vials in styrofoam to insulate against freezing thawing cycle of no frost freezer.

Any other useful info would also be appreciated.

This thread helped me a lot:
Guide to Making a Frozen Yeast Bank

I use a 50/50 mix of glycerin and water that's been boiled and cooled. I fill up half of my 30 mL tube with the thickest yeast I can get out of my decanted starter. Then I fill the other 50% of the tube with the glycerin/water mix.
50% yeast (with a little beer in there too)
25% water
25% glycerin

The reason I mix the water and glycerin is because it makes it easier to boil, cool, measure and dispense into the tubes. I think I might have to adjust the glycerin in the mix down a bit though as they wouldn't freeze in my normal freezer -- had to throw them into the old upright in the basement in order for them to solidify.

So far though, the yeast have all been alive when I've gone to make a starter with them. Definitely a cool way to keep yeast around for a while. Between a combination of freezing and washing I should only need to buy my yeast strains once a year or so.