Advice on rubber seals, please

[PotatoSoup]

Hiya, this isn't a plumbing question but I thought you folks might be the best people to ask? I'm trying to secure a vent cover with a 3cm deep rectangular back box into a wooden frame on a wall, the frame is also 3cm deep. I can make the wooden frame and width and height. I'd like the vent to be held on by the pressure of a rubber seal attached to the inside of the wooden frame or the outside of the back box on the vent (I'm assuming the former would work best). Please could you recommend a good rubber type seal for the job?

 

[PotatoSoup]

Like that - hope that makes sense?

 

[PotatoSoup]

Gah! Sorry, typo - I can make the frame ANY height or width (to accommodate the rubber seal)