I have a 22 and had the same problem. I ended up cutting a hole (yesterday 5/24/10) and added an inspection plate directly over the screws. After monkeying around, I think it was the safest way to go.There was no way I could get my arm through the plate by the gas locker, especially with a tool. Those screws are about 3" long, with a washer and nut. It looks like the actual thickness where the screw passes through the transom is about 1". Even if you could get your hand in there, it would be difficult to get anything done, there is not much room in there and the screws are close together.
The inspection plate is the way to go.