In the cube 2 documentation I saw that they used mapmodels to trigger the end of levels and loading of the next. Right now the only model in the game is the teleporter but the next release will have some.
Here is where it is in the docs.
http://sauerbraten.org/docs/editref.html#_mapmodel_To make a map config you make a text document and rename it to mapname.cfg so level.ogz, the config for it would be level.cfg
Here is an example in a map I saw for a level change:
alias level_trigger_40 [sp mpsp6b]
In there I think sp refers to it being single p_layer_ and mpsp6b is the map name. I think we'd just put in the map name and leave the sp out. Let me know how it works out. Take care.
-mike