Easiest way to sand super small areas?

I have a project for school and I made a shark-car concept. We were only given a 3" x 3.5" x 9" piece of super high density foam (its pink and its name sounds like "modulin" but that spelling isn't right). The sides have gills that are about.75" wide, 1.5" tall, and roughly.25" deep, faded up to the next gill where its a sharp drop off leading to a fade and so on. Look at the link at the end of this description for a picture of what I'm talking about (keep in mind the ruler is covering the top part of the car, it doesn't just cut off right there). The first picture is of the side I spent about 2 hours sanding (just for the gills, not for the rest of the side of the car), the second picture is of the other side that I just used the Dremel on, the third picture is the just second picture before I rotated it. So with all this in mind, what is the best way to sand in those tight spots? Even after 2 hours of sanding you can still see some of the Dremel imprints so how could I get rid of them effectively, and preferably in the most time-efficient way possible. Any suggestions will probably help considering I did so much sanding yesterday on the entire car (except the unsanded side) that my iPhone 6 no longer recognizes any thumb print because I have sanded the tip of my thumb just by using sandpaper and sandpads (sandpaper with a soft cushion-like side), at this point any time I save is helpful and my fingers hurt.

Your link doesn't work.

Use a small block of wood and wrap the sand paper around that to save your fingers.