I've used sheets of clear acrylic. at the moment these are simply cut to fit and tacked in place with cable clips, but eventually I will do it properly with magnetic tape, so that there is a better seal and yet easily removed for summer. The added glazing is completely invisible but makes a big difference to heat, drafts and condensation.
More expensive than the shrink-wrap approach, but well worth it.
...Oh and my house was built in the 40s too...1840s!