Morton, the DIY option is the better choice. Reason being you can make the dewshield to also extend the whole length of the OTA as this will help insulate the OTA there by eliminating the internal tube currents, and at the same time e tend the dew-free period fpr the corrector plate.
An off the shelf dewshield won't do thi s for you.
The car sunscreen material Wavy suggests is blooming brilliant for this! It is a very good insulator, perfect for this task
Alex.