I covered the vertical tail of a new model with some very light, but old silkspan.  It was fairly tight when I finished (dry covering).  After spraying, the covering wrinkled up like the inside of corrugated cardboard. The whole thing covered with fine, linear wrinkles. 

Any ideas?

I stripped that covering off and just went with SLC.

Way back when, you could dry cover with tissue and it would shrink tight. This was OOO super light material, and too fragile to do wet covering.

On another model I tried to use it wet and it fell apart. I guess it is just too old to be useful.

SLC over it was the plan, but it was so wrinkled, I just removed it and went with unsuported SLC.  We'll see how that finishes up as it needs to be painted. 

This potential disaster is part of the ongoing P-51 electric review article for Aero Modeller. I am really looking forward to finishing the project!