Thanks a lot for all the help. I got a fully adjustable heat gun from the hardware store. It has stepless adjustment of heat from 100 C to 600 C. On scale of 1 to 10, I have it set to about 3. At that setting it contracts the wrinkles with the nozzle at just under 2 inches from the surface. Works great.

There were many really big wrinkles on the bottom surface of the stab and I got them all out. After the final step of bonding with the iron, I immediately put the stab under the stone floor tiles with 15 kg on top. The "inverse camber" bowing flattened out completely, but then I noticed a little anhedral. I think that resulted from having the weights too much toward the center. So after a second go with the heat gun and iron on the flip side, I distributed the weights evenly over the whole surface. Now both the camber and anhedral are gone. Whew!

But I find that it's necessary to always use the 15 kg even compression on it immediately after treatment (it's a solid balsa stab).

There are a few minor wrinkles on the vertical stab. I'll use the same process (with weight compression afterward) on that.

Cheers and thanks again