I have 12" inflatable with a 9.8 mercury on the back. I was wondering if anyone with a similar setup could tell me what the best way to trim the motor would be for better performance. Currently I have the trim pin out, and the motor in the full down position, would I benefit from angling it outward a bit? Thanks

Alex buddy we meet again. You've made a mistake by removing the tilt pin please put it back in, you need this pin for 2 reasons
1. To set boat trim.
2. For the reverse lock mechanism.
If you remove the tilt pin the reverse lock won't work at all and the propeller will come out of the water when reverse thrust is applied not what you want to happen at all.

The tilt pin also sets the angle of the motor to the boat, this angle is known as trim.

When you trim a motor you are changing the angle of the boats hull in proportion the to water surface, ideally you want to raise the boats bow above the water line to create less drag on the boats hull thus producing more speed, better fuel economy and to get the boat up on plane quicker.
To set the trim put the tilt pin in the hole closest to the transom. (Trimmed In) now test-run.
If the boats bow seems to plough the water you will need to move the tilt pin further out (Trimmed Out).
Only move the pin one hole at a time then test-run again.
Keep trimming the motor OUT until either the boats bow is too high in the air or you find the boat is becoming unstable and hard to control.
Trim the motor Out the furthest you can this is where the optimal preformance if found.

P.S. Some-times If I find that the boat is trimmed just a little to far Out I will shift some weight to to the bow by moving the fuel tank, anchor or persons forward.

NOTE: By trimming your boat properly you will find handling and preformance is greatly improved.

Happy boating your inflatable buddy.