Replaced mine with a Mini Heki.. such an improvement over the old Hymer one that had gone yellow.. ..
It opens fully and lots of light floods in.. comes with a insect screen and black-out blind .. bought from Leisureshop direct..
you can also have it fixed or non -fixed ventilation.. I chose 'fixed' ventilation it is part of the ventilation system to prevent condensation.
word of advice, the Hymer window is 39 x 39cm . so I had to cut about 10mm off the roof aperture on two sides to get the Heki to fit .. otherwise a very easy job.. biggest part was cleaning off the old Hymer black mastic ..