Hi ,
I had a similar situation , ended up buying a sheet of 1/2 " closed cell foam , used high temp carpet adhesive to glue it up ( Roof gets hot in summer even in UK) , and then covered that in grey van lining carpet , which is quite stretchy and moulds well into the curves . All requires a bit of pre planning , and patience and a spare pair of hands helps . I made a paper template to make sure I got the cut right first time, and did a dry run with the closed cell , using the roof gutter to keep the foam in place , and it hides the edges . Can be done to look really good , I'd say better than than the factory trim ,
Good luck