Left wing tip.....rear most.
OAT probe bottom wing skin, next to access panel.
OAT wires into the Remote compass, so has to be close.
This set up worked great for me.
Magnetometer is mounted on the little "deck" just under the leading edge of the vertical stab. Wrap it in a plastic bag prior to mounting to make sure no water can drip on it from the stab.
OAT probe is mounted under the horizontal stab. This setup has been flying on my RV-6 for a few years and works very nicely.