I asked this same question a while back when I got my 15hp Yamaha. Several people told me that even though it was a manual trim, I could still use a standard transom saver. This is not exactly true...

If you search for 'transom saver' on cabelas.com and click on the Swivel-Eze transom savers, you can see that they look like they would work, but they way they adjust, there are only a couple holes that you can stick a pin through.

So if you tilt your motor down to the desired position, and the length of the transom saver does not match up with the spot where the hole is, the length will be wrong and your motor will bounce up and down anyway. On mine, it turned out that by pure luck the hole was in the right place. I still get a little bit of wiggle, but not much.

You could perhaps drill a hole in the transom saver at the correct spot, but you never know about modifying a piece of equipment like that.

I have seen people do things like inserting a piece of hard foam between the transom of the boat and the shaft of the motor, then strapping the motor to the boat using various straps, bungee cords, etc. It looked ok, but I don't know if you can get the parts to really fit your setup correctly very easily (think random trips to the hardware store trolling the aisles for appropriate pieces of foam).

Basically, I wished in the end that I had bought the 20hp Honda with electric trim. So much easier to just pop the transom saver in place and trim down to it. With my setup now I have to brace myself under the motor, holding it up very firmly while positioning the transom saver and slipping the pin in.

Someone will assuredly post now and explain some very simple method for preventing the motor from bouncing during transport with manual trim motors, but I don't know what it is....