Peter,
I bought one of these for instant use in 4/4.

Black Car Seat Gap Storage Box Organizer Phone Card Cup Holder Slit Pocket U https://www.ebay.co.uk/itm/-/403328772814

Fits straight in & looks ok, less than £7....

Jack
1985 4/4 T/C 4 seater Royal Ivory
1934 F Type
2018 Pembleton SuperSport (self built).