I found Torquay chandlers listing Talamex "covy" covers. The sizes and spec seem the same as the Trem covers.
I suspect the are the same just diffent branding.
The XXL is £50 cheaper too, but dont list the Maxi sized one. I measured the boat and the width of the XXL will be fine, but i dont think it will be long enough to fit over the A frame.
I might commission the misses to sew in some zips or velcro
Talamex 'Covi' Boat Cover L- XXL from ¬£69.24 - Torquay Chandlers
(They also have a tempting price on a M-Tech VHF radio at £85 too!)