I have been thinking of that lately and wonder if the bubble wrap with silver foil on both sides wouldnt be perfect.  It is rigid enough that it looks like you can just cut a slightly large pie shape for the sides and push them into place.  And they coud stow flat up above the mattress when the top is down.  

http://www.homedepot.com/Building-Materials-Insulation-Radiant-Barrier/h_d1/N-5yc1vZbedf/R-100052556/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

--- On Sat, 1/22/11, Jamie Auch <jamie@KOOKYMATHTEACHER.COM> wrote:

> From: Jamie Auch <jamie@KOOKYMATHTEACHER.COM>
> Subject: Pop top insulation
> To: vanagon@GERRY.VANAGON.COM
> Date: Saturday, January 22, 2011, 10:39 AM
> I am considering purchasing
> insulation for my poptop in my '89.� Can anyone give me
> suggestions to what they have done? Thanks.
> 
> -Jamie Auch
> 
> Sent from my iPhone