John,
I've got the Autocom lead feeding the sound from the SPlll into the Autocom, & the Garmin lead feeding power from an 'always live' fused powersource to the SPlll. The Autcom lead, which works well, has a circuit board built into it & is expensive (I think it's meant to be about £30, but they made a mistake with mine & undercharged me

- City Slicker poo-pooed the cost of this in a previous thread, suggesting that the board should only cost £1 or so - he may be worth contacting if he's produced an alternative).
The power lead is connected to an 'always live' circuit so that you can program & generally mess about with the GPS when you're stopped without having to worry about battery life (which, as you may have found out, can be very short!).
I use the standard, non locked, Touratech mount. I though about ugrading to the lockable one, but realised that, if I considered the unit was at risk, I'd take it off the bike and take it with me anyway....
Consider buying the carrying bag thing. It does a good job of protecting the unit and comes with loops on the outside to hold spare batteries and compartments to hold all your cables - not cheap, but good value IMHO.
MikeO
