You will need to put at least 1 window and 1 skylight for air circulation otherwise you will get dreadful condensation i am talking lots and lots of condensation that will make everything mouldy within 12mths
Boatingmanchester...sorry totally disagree with your advice...i left my bulkhead in and installed a roof hatch with no windows reason for that it doesn't look like campervan...if you do your research which i did glass creates condensation...i have lived 5 days aweek for 2yrs and no issues...leaving hatch slightly open during night is enough.
