Which engine do you have 3d-aholic ?
Your correct about the rust issue, chances are if the rockers and valve train are rusty so are the bearings & Crank,Cam and lifters not a good deal at all.
I run my engines dry after I get done flying for the day and if I know there not going to be used for very long I add some YS compatable after run Oil (approx 1 Tablespoon or more)and swing it over with the starter for 5-10 secs to get the oil all the way thru the engine. This helps alot to prevent rusting ,but I understand some folks purge the engine in afterrun oil, close up the carb, remove the plug and add oil to the top of the piston replace the plug and store it.
Make sure if you do this to get as much oil out of the engine before you try to fire it ,especially out of the cylinder. Hydrolocks can bend rods and create all sorts of problems.
Myself I have never had a reason to do this but its another option to help prevent rusting.