If the adults sleep upstairs the options open up quickly.
With the rear seatfolded as a seat and some cushions placed against the 
walls and the rear of the seat, two infants can be confined in the 
space.  We added a curtain across the opening from an old bus to 
shade the kids from our card playing lights.

Another option for a larger kids is to fold up the FRONT of the 
rear bench after it is folded flat.  It will stay in that 
position until it is push back farther to release the catch.  Worked 
when we added a third to the aforementioned pair of kids 4 years 
later.

An option for larger kids is to affix a net to the opening to the 
upper bunk to prevent rollover & outs.  Removeable of course.

For infants, check out carryable bassinets too.  Some of wicker, some 
of other materials, some folding.  Rather than a huge playpen.

- Jeff '80 Westi

> Has anyone come up with any interesting tricks to keep a sleeping 
> infant confined safely?