Yes, if the insulation's conductivity can be expressed as a function of temperature, either as an equation or as a set of tabular values.
I'd take as many datapoints as are available for insulation conductivity at various temps and then fit a curve to those points to get an empirical equation.
The area also increases with distance from the inside surfaces but I'd ignore that. Calculations like this are approximations at best anyway, because they don't take into account radiation or convection.
Ron Reil reports that coating the inside with some ceramic stuff that reflects radiation helps quite a bit.