I messed up my supplied D-seal and had to find replacements. My local store (in Sweden) had something that is probably the same brand and about 80% of the size from what Vans supplies, check your local store that carries seals for windows, boats and things like that. With some luck you should find something slightly smaller that will fit.
As it turns out, i must of gotten lucky when Van's sent me the original material. I was going to order more but I decided to see just how much was left over from the original shipment. Turns out it was just enough to redo by a quarter inch.
I only had to move it back in the flat middle section. Each curved side fit fine.
I had same thing first time I closed the canopy after placing that seal. I tried tucking it in as I was closing the canopy, had a friend with a plastic squeegee-type thing push it an as we closed canopy. After sitting closed for a while, It seems to remain where it needs to now. Will keep an eye on it, but it seems to work fine for now.
RV-14A in progress
QB wings and Fuse in progress