Just thought I'd post some details of my new cover for the Optimax as it's something I searched for, for quite a while and thought these details may be useful for anybody else on here looking for an outboard cover.
I got it from www.outboardmotorcovers.com
and they make covers for all Mercury/Mariner, Evinrude, Johnson, Yamaha, Honda and Suzuki outboards. Mine cost $98 including delivery from Canada.
The cover itself is a heavy duty, waterproof cover and is fleece lined and fits the engine perfectly as each cover is individually made to fit your engine. What I found is very useful though is that the leg portion of the cover can be separated from the cowling cover so it can be used on a mooring also (saves cleaning all that bird crap off!!)
Only thing was delivery took 6 wks, but it was free so who cares!!