No limit on length - other than the 7m body length for vehicles up to 3500 kg.As Lutz said there are plenty of large SAs available. Quite a few at 8’ wide too. Are you limited by maximum length ?
If we went for an island fixed bed caravan, it would have to be 8' but a 7'6" luxury 2-berth would also work for us, if only they had adult size berths of 6'3" - build quality is paramount but Google AI seems able to identify common faults at all levels across all brands I've checked so far - it seems all the premium brands are chasing volume and profits while the luxury brands like Carlight and Vanmaster have long ago gone to the wall.
Sadly there's too many glaring design faults even at the expensive end of the market.