Dinghy Cover ?

[postlapsaria]

I recently acquired a fiberglass dinghy/rowboat that's a little under 8 feet in length with a beam of a little under 4 feet and is powered by a trolling motor and battery. It looks pretty similar to this: http://i38.tinypic.com/2e4ffrs.jpg

I'd like to keep it tied to my dock (rather than flipped over on my lawn like it is now) but I don't want the battery and motor to get rained on or for the boat to fill up. Problem is, I can't seem to find any boat covers out there that would fit. The only covers I've found that are small enough are either for the wrong style of boat or are custom covers that cost nearly twice as much as I paid for the boat itself. So I was hoping someone here could offer some advice or point me in the right direction of where to find an inexpensive yet effective cover that would fit a small dinghy like this.
thanks for any help!