1. Yes there will be tons of styrofoam bits everywhere, I did the install with the door mounted and put a sheet over the screen and bits still got in the pod and covered everything within a 25' radius of the pod.

2 I also used a fine tooth blade and made sure it was a long one.

3. I cut from the outside, the blade will wander ,go slow and don't force the corners or it gets worse.

4. After I did the cut out I used a large file to shave down the cut out wanders, and then a 60 grit sandpaper on both the outside fiberglass and inside plastic veneers to fine tune the opening.

5. Large bead of silicone on the frame,which gave me a nice squeeze out bead . And then I carefully cut it off after it dried.

 Pretty east install if your handy at all.

rgds John

If you figure out a practical way to get at the window without having to open the door, be sue to post it.  We have the same access issue with our marine porthole, though it's small enough that no curtain is really needed.

or search this, RV ENTRY DOOR WINDOW FRAME TINTED WINDOW PLEATED SHADE LCI 

These windows are $99 with free shipping.

 I got this one because this is what she wanted, To be able to see out and then still have privacy.

They came off a bunch of new, mis manufactured doors, they are NOT perfect brand new, still inbox windows.

I was a little disappointed because there were a few small, Light, scratches on the glass and frame, and the frame had a small sun-bleached spot, (Mostly Rubbed out ok). 

But once it was installed it looked as good as the other windows, and I can only see the minor scratches when I am cleaning the window. (you get what you pay for).

 All in all worked out well. The frame and trim are plastic.

Voisj

Nice work! 

pull down blackout shade. Taped it , marked it, drilled pilot hole, cut with jigsaw, installed it.

Took an hour, Thanks for the tips!!

And then my wife says, "but you have to go all the way outside and then close the screen door then pull the shade and then open the screen door go back inside and shut the door?... huh" 

The porthole is secured closed by two hand star nuts that are about 1 1/2" in diameter.  They fit between the screen door and the hard door, but only barely.  They do press against the screen, but not enough to cause a problem.  

Marine portholes swing up to open and the bolts and hand star nuts drop down out of the way.  You can buy screens for them, but it really isn't necessary since the screen door functions as a screen when in the open position.

One of the biggest problems with window flange is about just long enough to fit through, but just barely.  When you tighten down the ring flange which goes around the outside of the window, it is just barely covers the window flange, leaving a flush surface, but you end up compressing the door a bit to get a good seal.  After installing mine, I developed a horizontal crack on the surface of the inside of my door centered on the porthole.  It doesn't hurt anything, but it indicates that there was some stress that had to give.  

If I had it to do over again, I'd have bought the window from the supplier mentioned in this thread, but at the time, I didn't know about them.  

I got my window on Amazon, I like the fact that it opens. I had no chipping at all on the fiberglass.

I would go with the router if you can. I used a jigsaw and figured any damage to the fiberglass would be minimized by the cut pulling the fiberglass up into the Styrofoam backing so I cut from the inside. To my horror I discovered the blade wandered outwards on the corners, and the frame barely covered the opening on the outside. I used a heavy bead of caulk and haven't had any leaks, but if I did it again I would cut from the outside, or go with a router. 

Also, remove the door, it is easy to do and is very light and easy to handle. It is a lot easier working horizontal than vertical!