I am looking for a suitable roof vent/skylight for a 1982 Devon, The PO took the old vent out and put a bit of perspex in place, I am happy with this as it is watertight and flat with the roof but the other day we used the van and my daughter slept in the top; she almost past out with the heat from the sun

So I want to try to find a replacement vent that does not stick up too far so it will go in the garage (7ft opening).
A few questions:-
Are caravan vents suitable for a angled pop top roof?
I think the vent is a 15" x 15", does anybody know the actual size I need as i don't want to cut the roof out.
Most of the roof vents I have seen are a big bump on the roof even when shut I think this will be too high. Can you get slimline vents??
Thanks for your help

I have just measured the old fly screen that the PO left with the van, it is 13" squareto the outside of the frame if that helps.