Hi Ian, Dead easy to replace skylight, if they are of the 400 mm push up style, simply unscrew the handles from inside your 'van and the s/light will drop down, installing a new one is just the reverse procedure
Jack, Cornwall, May 2009
If the standard type not the modern day larger ones yes easy just done mine. if leaking through screw holes of the cover the just replace the cover.
If leaking from the frame re-seal on outside edge you may not have to replace the cover.
I case it is the cover.First take digital picture of it closed and open so you can see positions of the stays on the handles. Unscrew the stays pull them away frome the lugs they are on. The cover will in most cases come with new handles fitted leaving you just to fit the stays on the lugs. You might find this a bit difficult I thought it was the wrong one but ensure they are fitted as the old ones. if you get black additions catches I didn't bother fitting them they were a pain. If not special one but standard the toilet is the smaller of two they only seem to do two sizes one for the toilet and larger for the saloon area. Take the old one with you and you can't go wrong.
Good luck