Thingy said:I have heard of but never used a product called "creeping crack cure". I understand its suitable for the outside panels of the caravan but may be a temporary repiar for the window.
Liquid sealant/adhesive with exceptional penetrating properties
Travels deep inside the narrowest of cracks before making a waterproof seal
Traces and seals leaks caused by hairline cracks in the home, boats, motorhomes and vehicles
Quick and easy to use - no dismantling of parts required
Dries transparent and flexible
Cant recommend it as I have no experience of it.