I must be getting wimpy lately cause I sure have trouble getting the hatches off and on my Valley Aquanaut. They really keep the water out but they are so tight you risk tearing your finger nails out every time you open them in cold weather when the rubber is harder. And putting them on tightly can be so hard that it is tempting to just leave them half loose- not a good idea. A lot of my friends carry a little piece of wood (1 1/2 by 3/8 by 4 inch long works) to push the edges of the cover down into the slot. Anyway, I came up with a modification of a plastic bucket lid opener which is available at most hardware stores. Check it out-- http://homertide.blogspot.com/
Any other ideas? Happy Holidays!