OK, I just posted this on another thread, but it still works here.
Look at your local hobby shop. Most sell rubberized CA (superglue). It's black, and works great. The rubber in the glue makes it less brittle than normal CA. The R/C guys use it on their cars and planes because it better resists cracking due to the vibration of the motors, and bumps or whatever. It sands well too, and is great for filling gaps.
I used this on vinyl kits and it works great!
Good Luck!
Brian