To sand coves, wrap sandpaper around small lengths of clear flexible plastic tubing. Most hardware stores carry this type of tubing. Choose a diameter smaller than the radius of the cove. Slice the tube down its length and slip one edge of the sandpaper into the slit. Then wrap the sandpaper around the tube and hold it tightly.
Several methods are available for dealing with screws that tend to vibrate loose on covers of equipment such as chainsaws. One good fix is to remove the offending screws and wrap 1/2-in.-wide Teflon tape around the threads and then screw them back in. The tape will hold the screws tight, yet will allow you to remove them when necessary.