Jails setup with binary packages only

[Guy Marcenac]

I would like to use a freebsd system with binary packages only. I want 
to heavily use the jail concept. All the documentation about jails 
implies the use of buildworld into the jails.

In order to avoid any compilation time, I installed a minimal base 
system for the host and I nullfs mounted read-only every system 
directory (bin, sbin, etc) into my jails. Then, in order to be able to 
install additional software inside the jails, I unionfs mounted 
read-write empty directories ontop of the nullfs read-only system 
directories.

So I only have to freebsd-update the host and then freebsd-update each 
jail in order to keep updated.

What about this kind of setup ? do I miss something ?