Fiberglass tape ( at wal mart in the dry wall area by the paint) and shoe goo. Found by the shoe laces cheap fix.
If u want to do the out side so u can sand for a flush crackless look u can use bondo.. then just paint over it.
Biggest thing is the crack MUST be repaired before covering it up. I use a solvent type glue to adhere the pieces back together. You want an ABS/styrene glue like Plyabond (sp?) or tenax. After the repair back the crack with a piece of scrap styrene that overlaps the crack about a 1/4" on both sides glues on with the same solvent. I like to cover that internal part with a final layer of a flexible adhesive like E6000. After you have a solid base again sand your area for repair on then outside and lay down some automotive Bondo like Chase said. Don't try the paste,glaze, spotting putty,JBweld or anything just plain 2 part bondo. Sand it down, feather it out, prime it, sand it more with fine grit and lay some paint. it will be like it never happened and shouldnt be a problem again as that area usually is stronger than the mating areas at this point. A small word of advice with it all is PATIENCE!!!! the time you take reflects your finished project. If you can after you lay the first coat of bondo let it cure a day or 2. Body fillers are somewhat unstable at first and in some cases can take weeks to fully cure.
