Installing vent fan on conversion van top

[TOMMY47]

I have a conversion van with fiberglass top. No hole in roof. I'm thinking of adding a reversible, electric vent fan.
Anyone know what the typical distance between roof and inside liner is?
Is it a difficult job to safely cut through roof? This does have an AC unit on the roof.
What companies make a reasonably priced fan unit? Not gonna pay $250+ for a Fantastic Fan.

[scbwr]

Have you considered that you need 12 volt wiring running to the fan?
I would tend to think that any space between the roof an liner would easily be handled by the inside trim piece that comes with the fan. They are designed to be cut to size and for any pitch of the roof. But, I have no idea what you would find when you go to cut through the roof. Hopefully, someone can provide some answers.

You can buy a decent fan for under $150.
Fan-tastic fan at Amazon

This one reverses!