Chris... I used burlap last year, one big problem with burlap is if it gets wet and freezes, you are SOL. The burplap becomes a solid burlapsicle!
I just purchased some acrylic military surplus desert camo mesh netting, I am going to make my cover out of that, then zip tie some rafia grass on top to break up the outline.
Do a search for outboard motor covers and my name and you will see the setup, someone suggested it to me and it looks pretty good.
Boat looks great, but yes... that grass will break down and wilt after awhile. I used similar grass on my boat and never extend it more than about 15 inches past my cockpit doors or by mid season it just falls over. The great thing about duckboats though, is you hunt a bit and learn a bit... The more you use the boat, the better ideas you will come up with... thats all part of the fun too!
Good luck!