Thanks to Ray Copeland and Clancy Arnold, I have some 2 mil plastic bags to play with.  I made a couple of tanks with them and flew one today.  The performance was excellent.  Now I need to fly it for several weeks to evaluate durability.

Those of you with calipers or micrometers, sneak into the kitchen and measure all your wife's baggies!  We need brand names and specific items listed by film weight.

Clancy sent me some 1.5 mil bags, and I will also try them out.  Lighter is better, of course since the fuel will drain more evenly and conform to the container better. 

My Nelson Head/Brodak .049 does the full pattern on 25cc of 15% Nitro on 46' lines with a Master Airscrew 6x3 prop, just for reference.

Great input, thanks!  Keep those numbers rolling in, folks.   

I have used non-latex condoms FOR THE FUEL SYSTEM!.  Works good.

So far, I am still having a leakage problem.  If I overpressure the tank at all, it springs a leak.  No margin for error it seems with incompressable fluids.  I am also having a problem that the heavy baggies take up too much room and allow less fuel in the tank compartment because they don't seem to unfold all the way.  I may have to make a clear plastic box to see what is really going on.

For the contest tomorrow, I am going back to balloons!  One trick I do with them is to blow them up with air and leave them for a day.  They end up much thinner wall and larger capacity, but seem to retain adequate toughness.  Kind of like breaking in a rubber motor on a free-flight.