Hi Elly,
oops, I bet there was a few choice words?
you could try some clear all weather adhesive, designed for outside use, the type that is fully waterproof , mould resistant, highly flexible, sets under water one is very very strong (goes off quickly) - available from proper builders Merch.
apply a small bead to the frame and material (use masking tape to ensure it does not get everywhere) ideally near the open end of the rip.
the first stage it to get the material back in position, to allow you to check your happy and create a bond for the second part.(Only a very small bead is required initially to fix the open edge in place.)
using two pieces of wood , or something suitable to create a sandwich effect and not Mark the blind / frame , apply masking tape to any parts that may touch the glue, including the frame and blind itself, clamp the two pieces of wood along the edge of the frame, to create a sandwich effect, the sandwich will hold the ripped section of material in place whilst the adhesive go’s off, to create an initial join to the open part.
remove the clamps and inspect to ensure a satisfactory bond of the open ripped end (after the adhesive has gone off) clean up any excess.
if the initial bond does not sit right or is not visually good , cut the bead and try again.
once you are happy with the initial bond and how the material looks :
repeat the above with a full bead of adhesive o along the ripped section (ensuring the wooden clamping pieces) has something applied to it to prevent to glue bonding to the,
take your time and be scrupulously clean , if the glue gets on anything it can only be removed mechanically (possibly peeling any residue once set)
edit you will need to prevent the blind retracting whilst you work on it , consider using wood batons clamped to the fully extracted blind , you may be able to use the multiflex, door table etc as a work surface inside the van, so the blind is not left hanging
edit: something like this, I agree with
@The Tall Luthier that super glue may assist in creating the initial bond to the open end, but superglue will not hold up over time so will require something like a strong clear adhesive- see photo below, something sI ial to this as a permanent glue
View attachment 96159
View attachment 96160
