alright so if its hollow youre going to have to fill it with something so there is some "meat" to secure the pieces together
you can either use resin (costly and would be heavy) or you can use expanding foam (inexpensive, lightweight but can be messy and not as strong)
your best bet may be a combination of the two put the expanding foam in just enough that it rises to about 1-2 inches from the broken seam (be careful this stuff goes a long way and is very difficult to remove once cured). fill the rest with resin or even apoxie like aves so that there is a rigid material to pin
you will need to pin the broken parts together, I like to use threaded rod so the apoxie has something to grab onto. there are many tutorials on this but basically you drill holes in both the pieces you want to attach, put apoxie in both holes then the threaded rod and attach the two pieces either using additional apoxie or super glue if you can to hold the pieces in place. 24 hrs later you can go back and fill in any remaining gaps with apoxie.
sand smooth, prime and paint