John, the 540 cover came in two heights, the later from 2010 being for the taller vans. It would be a good idea to let members know the year of your van.
If you do not have any luck I can recommend the Kampa range. They do a generic range that I've used for several years. They also did an Eriba specific model but I cannot remember when I last saw these advertised and in stock.

Colin

John, this shows the generic Kampa cover on a 2017 Triton, and I believe it might fit the Troll body length as you have extra material available on the width. If you have a look at the last photo then you will see the stock code and sizes.Kampa Prestige [generic] Caravan Cover These however imply it would not fit.
My current van is a Feeling, with a 486cm long body x 217cm width. I bought the 14'-17' model, which is 4.25 -5.20 m and stock code 9120001938. Your Troll has a body size of 471cm long x 210cm width so I think this would be a better option if you cannot get the elusive model specific Kampa model that I cannot find online.
As with any generic cover there is some compromise. I've found over winter I wrap extra straps around the waist of the van and tuck all the excess fabric in tight for the winter gales. For the rest of the year when the van is in use I simply keep the cover thrown over the van and find I can unzip the corner to gain access.

Colin

I've found the Eriba specific model, in stock and on offer. https://www.attwoolls.co.uk/kampa-eriba-...r-troll-feeling
It looks like it is suitable for the 530 and 540 as the roll up area for door access is double width.

Colin