Well, here's an update. I have it working. This is the stage I'm at now.
I got the Durovis Dive 7.
https://www.durovis.com/product.html?id=5

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It's pricey but my mate gave me the tablet so I thought I'd treat myself to something sturdy that will fit well and not pull down on my face. I had to mess about with the lenses for the correct IPD (distance your eyes are from each other) and have ordered some reading glasses with a magnetic nose piece that pulls apart that will fit in as I am still a bit too long sighted for prolonged use. I can bend the arms out and poke them through the holes in the sides from the inner side and snap them together at the nose

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So I've been using Trinus Gyre (
http://trinusvr.com/) with the Nexus 7 (2013) USB Tethered and in Aeroplane Mode. Games have to be played in 'Windowed' mode for this to work. Bear in mind I have a low end GPU (EVGA GT740 SC (2GB)) and all my results would be improved significantly with a better card.
There is a setting on the Trinus Gyre (TG from now) called 'Fake 3D' and it simply splits the screen with duplicates of the desktop picture so you have the impression of a single image streamed to the HMD (Head Mounted Display), when looking through both lenses. To get Head Tracking TG has a settting that uses the tablet's accelerometer and gyroscopes and converts it to mouse control so in ED you can set up Head Look with mouse (TG also has several other HT options including one that uses Free Track and a setting called 'Track IR Fix'. I've yet to try these). This worked really well and there was virtually no lag at all. I was looking round the cockpit and about the canopy, following my adversary's every move and pitching and rolling to meet him with my lasers. There was no real sense of depth compared to 'real' 3D but the effect is pretty astonishing all the same.
To solve the matter of 'squashed' images I made some custom resolutions in the Nvidia control panel. Doubled the second figure to elongate the apparent lines and stretch to compensate. They are 1280 x 1440 and 1920 x 2160. They both work a treat but the latter is too hard on my GPU.
Now on to 'real' 3D:
This, I knew, would get laggy on my GT 740 but I had to try all the same. So I switched of Fake 3D on the TG Server and fired up ED and selected Side by Side in the game's Graphic Settings. After fiddling with the 3D Seperation and Focal Distance (for me the best was both all the way to the right) all I can say is
WOW!. In the training missions 'Target Practice' I rolled up to an asteroid and just sat there looking up through my canopy, probably dribbling, thinking 'THAT IS HUGE!'. So of course I had to do the 'Travel' one too. I just spent ages inside the station then going to the Outpost and 'Buzzing The Tower' and it was all so big.
My GPU would only really work albeit a bit jerkily on the 1280 x 1440 res and the text is totally illegible so serious online gaming is out of the question. On 1920 x 2160 the graphics looked great and the text was really clear so, with a better card, this is a serious proposition for 'proper' gaming.
So there you have it. Home made VR is possible. I know nothing about coding etc (unless you count BBC Basic 30 years ago) and am quite new to PC gamng (built my first PC last October to play ED) so pretty much anyone should be able to do it.
Oh, and for anyone interested The Durovis Dive 7 (Tablet) and 5 (Phone) can be downloaded for 3D Printing so you just have to get the lenses if you don't want to buy the HMD.
Fly Safe Commanders!