Just re-read your opening post! You say:
"The downside I have just realised is that the canopy is rolled in bag around a pole, the length I would need would be 3 meters. Although the bag slides onto the awning rail easily it does really need to be fitted onto the awning rail when leaving home simply because the 3 meter long canopy on the pole would not easily fit into the van".
Re-reading this makes me wonder if you have understood the "canopy in a bag" concept. Not being critical but hopefully helping.
The canopy itself is a sheet of fabric/plastic/whatever. One of the long sides is permanently sewn into the bag. the other end is fixed to a hollow tube.
The hollow tube (or similar) holds the two front corner upright poles. In my Caravanstore they slide inside the tube.
What you can't do is separate the bag from the canopy - they are one item.
To mount and dismount you need to have the full canopy opened out. The bag end is now flexible to be fed into the awning rail. You probably have a helper holding the metal tube with upright legs inside and keeping pace with the bag's progress into the awning rail.
In addition you must have a straight length of rail for the canopy to fit.
If you don't mind going through this process then you could mount and dismount the whole canopy and bag every time you stop. That would totally negate the vast advantage which is speed of erection and putting away. And you would probably trip over the thing inside the van!
On the matter of putting away Mr Grumpy mentions the "complete pain of putting it away".
Again it's horses for courses. The weight of the tube and the canopy is not trivial. You are rolling the thing up and raising as you roll until it fits inside the bag.
My wife holds one end and after sliding the corner upright inside the tube begins to roll it all up with an "underhand" motion. I do exactly the same with the other end.
The caravan step has already been placed near the side of the van at the center point of the canopy bag. When wife and myself have would up as far as she can reach I move to the center of the canopy and standing on the step continue rolling until the velcro strips sewn inside the bag are positioned around the rolled up canopy to hold it in position inside the bag. There are further velcro strips at either end but once the center strip is in position this will hold the canopy by itself.
If you can lift whilst rolling around 10 kg then putting away is not difficult. A 3m canopy that you are interested in will be lighter than 10kg I think.
On the continent I would say many more vans carry a canopy of some sort - in bag or wind out - than you see in the UK (Motorhomes excluded). They are ideal for speed and offer good shade. We have an end panel which is similar to a mesh and this will cut out the worst of direct sun. A similar much shorter version an be popped along the front tube (Yes, the tube of the Caravanstore not only carries the front legs but there are two channels running its length - one for the front side if used and a second channel for extras such as the sun shade.
Phew. I'll shut up now. Sorry this has been so long winded. Good luck with whatever path you take.