You can put them anywhere you want, Viper.  I have a V4 external runtime, a V4.1 external runtime and a V4.2 external runtime because, obviously, I started with V4 and went from there.  I did install the original V4 into my P6 and P7 runtimes.  I did the same with Aiko 4 even though I have an external runtime for her, as well.  Any character packages I buy or make go into external runtimes.  I hate installing to the main Runtime because it can get bloated really fast and then Poser takes forever to load.

Hugz from Phoenix, USA

Victoria

Remember, sometimes the dragon wins. Correction: MOST times.