Just a few other points to consider also.  The silver bubble wrap
reflect radiant heat to the inside and outside which increases it's
effectiveness at keeping the heat in or out.  I doubt that with all the
other sources of heat entrance or escapes that it will make much
difference what is used, but the foam material is definitely cheaper
that the bubble wrap.  Whatever you use do not use anything that can
hold moisture like the OE fibreglass stuff.  I did not glue my
insulation in place as I wanted to be able to easily remove to
re-rustproof.  Also, I did not bother with vapour barrier, way too hard
to do a good job in the westy...too many factory holes everywhere...and
I like the holes and gaps to allow any moisture that does inevitably get
in to get out fast in.

BTW, nothing beats a good sleeping bag and another warm body to keep
warm while camping ;o)

Pascal
'84Westy