I agree with Nate, the heat required for melting PLA and ABS is at a minimum 180c / 350f, so I don't think that would be a problem. Besides, how many geese spend much time in the sun unattended these days?
I may also try my hand at casting with silicone molds. Messy, but it could produce clean pieces.
The center large piece needs to be somewhat flexible to get the fins into place, so combining the two large pieces into one probably wouldn't work well. Fixed fins would allow all pieces to be combined into one though.