We have had a similar problem, most recently this past Labor Day
weekend.  I was anxious to check the postings to see if anyone else
had reported problems with bats since no one I have talked to has had
or can believe the problem we have had.  Here's what we've
experienced.

We have had Coleman pop-ups for the past 14 years or so.  Our current
unit is a 2001 Bayside (that we are now thinking about renaming the
"Batside.") Last summer at Wilderness State Park in Michigan we woke
up in the middle of the night hearing something flying around inside.
Being half asleep I saw it on the screening of the end window and
thought "That's the biggest moth I've ever seen."  Swatting at it I
realized it wasn't a moth but a bat.  Luckily I was able to zip up the
canvas quickly, trapping it. I held it in place with one hand against
the canvas.  Then with the other hand I unzipped the canvas with my
other hand (gloved), grabbed it and tossed it outside.

The next day I found a spot where the canvas had pulled away from the
clips that hold the side tenting to the top of the camper near the
lift mechanism and assumed that this is how it got into the camper.
My wife continued to hear bats fluttering outside each evening, but
none got in and I thought the whole episode was an unusual, isolated
incident and wouldn't happen again.

Following that we had other camping trips without incident. This past
weekend we returned to Wilderness.  Again we heard bats outside, but
I'd checked the canvas clips and stuffed any access holes I could find
with towels, etc.  While sleeping one night we heard a scratching
sound, but were unable to find the source and there wasn't anything
inside.  The next evening we again heard the sound while playing
cards, but now we were able to isolate it to a space where the side
tenting connects to the top.

The Bayside has the typical end bunks and also a pullout dinnette and
a pushout kitchen window.  When you pop up the unit the tenting which
is attached a few inches up inside the top pulls against the edge of
the top and effectively creates a small tunnel with an entrance on
each end. Thankfully these are outside the camper. From the inside of
the camper you can run your hand along the tenting at these spots and
squeeze the tunnel closed.  When I did this I could feel a bat in
there and could also feel it work it's way out.  Outside I stuffed
towels into the "entrances" for the bed ends.  Next day I wondered
about the tunnels by the kitchen window and dinette and decided to
check.  Sure enough, there was a bat in the tunel by the kitchen.

We lowered the top a little, washed out the spots and the stuffed the
ends with foam and although we heard some fluttering during the night
we had no bats inside or in any of the tunnles for the balance of the
trip.

Since it's happened twice and both times at Wilderness Park I talked
to the ranger.  He was surprised and told me that reports of problems
with bats were uncommon.  We're now wondering if there is something
about our camper or our camp site that attracts bats? Is it the park?
Is there a way to discourage them?