I recall a thread sometime back about how to keep your pillow from falling
from the upper bunk. One of the more novel suggestions involved the use of
Velcro. Our solution was less inventive, but it has other benefits as well.

What we did was cut a board that basically is just an extension of the
fold-out portion of the upper bunk. The sides sit on the same rails as the
fold-out bed. We cut notches out of the front corners to allow the board to
fit around the support brackets for the pop top. The end result is a wooden
platform that reduces the opening at the front of the bunk to perhaps three
inches.

Pre-children, we found the board was a perfect place to place a
battery-powered lantern, glass of water, wallet, keys, etc. Put your pillow
out there and suddenly your feet don't hit the back of the canvas anymore.
(And your pillow will not drop into the abyss below.)

We just came back from a week camping in the Champlain Islands of Vermont
with our two children (6 1/2 and 4 1/2) and for the first time they BOTH
slept up top. And with the board in place, there were no concerns about
them falling from the bunk in the middle of the night.

Because the board is the same width as the bunk, we place it cross-wise at
the back of the pop-top for storage before folding up the bed and dropping
the top. Fits like a charm.

It's a decidedly low-tech solution, but works great for us!

--Bruce--