Never worked with an MGW cap, but assuming it is the same as the stock one, here are my hints: Remove the rubber grommet from the gas filler tube and install it on the cap first. The grommet fits onto the tube MUCH easier than the cap so it is eaier this way. Put a little lube on the filler tube before trying to pop the cap/grommet assemly on (heck turn off the lights and put on some Barry White if that helps). My hands/arms are really small so what I do is reach my hand through the body and grab the filler tube "inside" the car. You can then pull it out quite a bit (there is flexible hose between the tube ad tank) and work the cap/grommet onto the tube and then slip your hand out, rotate the cap so the screw holes line up, put the screws that hold the cap to the body back in and you are done. If you cannot fit your hand through the body hole, consider asking you wife for help as pulling out on the tube makes it SO much easier to pop the cap/grommet on to it.