Published another document today on configuring internal / external DNS for use with Session Border Controllers. It's got a bit of a sipXecs slant to it but should be useful for others looking for redundant and load balanced SBC setup help.
It is available HERE and HERE2
YMMV with Asterisk & FreeSwitch installations and SRV based authentication methods... Most of the setups I have seen are A records pointing to the PBX.