You might also consider a thermarest or kelty air mattress.  When I  hike I
use a 1/2" thick, which is borderline, but if I'm camping out of the car  I
bring the 1-1/2" thick.  It rolls up to about 24" x 6", and is so plush  I've
awoken in campsites and thought I was at home in bed.

hth
rob infante

In a message dated 7/6/2005 5:12:50 A.M. Eastern Standard Time,
inua@CHARTER.NET writes:

I'm  getting old joints and need to lay down a mattress pad in the van
when  camping.