Hey-
I actually take mine off and lay it in the truck on the throttle/handle side (I use a a rope or bungee to keep it from sliding around).

A boat mechanic said that laying it on the throttle handle side does a couple things: It keeps any water from the lower unit from running up into the housing and engine etc. AND the slight tilt also helps keep your floats from sticking (It depends on the make and model though).

I take mine off because my transom is Fiberglass and the spot I had to mount it is fairly thin (I used a backer plate inside the hull) If you've ever seen those things bouncing on the back of a boat going sixty......You may want to consider removing it if you dont have a really stout factory or after-market mount.
I actually saw an outboard fall off of a guys boat on the road that parallels the Cowlitz between Blue creek and Barrier. It was heart breaking to see that brand new 9.9 bounce along the road surface, shedding parts and pieces......
Those trailer supports (as mentioned above) work good enough if you can get one to fit your trailer.


Phreak