Red actually matches well with a surprising variety of colors, IMO. Just think about how prevalent the color is in nature: Ahh, beautiful! Just my personal opinion, of course.
Honestly, if it where mine I would either go with a gold/bronze or a pure white... No fancy designs or graphics, just solid color. Doing the same in BRG might not be so bad either.
Not exactly sure what year Traveler you've got there, but if you're going for as authentic a period correct look you can, I'd suggest either a Snowberry White (WT 4) or a Black (BK 1) roof to go with that Sandy Beige (BG 15) colour. This is period correct for all MkII Cooper and Cooper S colour schemes. Your car appears as though it may be of Mk III vintage judging by the Leyland badge in the grille... Not that this is significant necessarily, however as far as I've been able to find, MkIII cars were typically painted all one colour. All that said, the beige/white combo was the lesser popular between the choice of a black or white roof. Your car is very nice as it sits, as others have said. But, I'd look at painting that roof black to change it up a bit. If ya hate it, you can always paint over it. Good luck with that great car!
It's a 1980 Clubman Estate, Firebro.... I kinda like the idea of the RAF roundel..... The car is champagne beige, not sandy beige, just FYI. It's an interesting color, it changes quite a bit depending on the lighting... Vinyl is a good idea, or plastidip - tho I hate the stuff, it would be an inexpensive way to see it in the flesh so to speak, and as you said if I don't like it, it peels right off. I was also thinking either dark red or green might work.....