Placing a Roof Hatch

Very important note: Before you start making holes in your bodywork, make sure it is allowed according the legislation in your country, so your van is homologated.

The hole
To install the roof hatch, you first have to make a proper hole. It is important to know the inner size of your hatch to cut the hole to size.
To make sure your hatch will be in the exact middle of your roof, you can measure the middle point from the inside of your van. Now you can drill a small hole in the exact middle from the inside to the outside. From this point you can measure and drill the corners of the hole (that matches the inner size of your hatch!) and finish it from the outside (this way you are less likely to get metal splinters in your eyes and it is just easier to saw downwards).
Tape the edges you are going to saw with masking tape to reduce the amount of metal splinters. Connect the holes with a straight line from corner to corner with a  jigsaw, specific for metal. As soon as it has been completely cut out, you first check if the hatch fits.
Fits perfectly? Then you can sand the edges with a metal file and treat it with an anti-rust agent to prevent rusting. As soon as the anti-rust agent is dry, you can go on to the next step: placing the hatch.

Make a wooden frame
Most likely your roof is not thick enough to fix the roof hatch securely. In this case you will need to attach a wooden frame on the inside of your roof to secure your hatch. Depending on your hatch it is possible that it consists of an outer part and an inner part. You have to check how much space you can leave between those two parts: It’ll determine the thickness of your frame as it’ll come between them.
The inner size of your wooden frame must have the same dimensions as the hole in your roof. Make sure you use wood wide enough so that it does not split as soon as you screw in it. Also the size of your screws is important as they have to be long enough but not too long either. Once your frame is finished you can fix it on the inside of your roof with polymax.

Make the outer part fit nicely
On the outside it is possible that your roof is ribbed so there are higher and lowers parts. As a consequence there will be some gaps between the hatch and the roof in some places. You can fill these gaps with small thin strips of wood so you don’t have to fill it fully with silicone sealant. Also in this way pressure will be divided equally.

Attaching and sealing the hatch
As soon as the inside frame is fixed properly and the outer part fits nicely on the roof, you can attach the hatch from the outside with the screws in the wooden frame.
Now it’s time to make everything waterproof with silicone sealant. You can first seal everything with a water resistant epdm strap and finish with silicone sealant. Once the outside is fixed, you can attach the inner part as well. 

Testing
The moment of truth! Once the silicone sealant is fully dried, it is time to test if you have sealed it properly. If there’s still water coming through, you have to use more silicone sealant. Make sure every slight gap is sealed. If everything stays dry, you did a great job! You now installed your own roof hatch!

If you’re not sure about placing the hatch yourself, there’s always the possibility to outsource this job. In this way you can be 99% sure it is done properly.