It sounds like you want a small driveaway awning, there are hundreds of different models available, have a quick Google or have a browse on ebay and you'll get an idea of what is available. You could also consider using a utility tent, we found that gave us plenty of extra space and we didn't have to line the van up perfectly every time we came back to our pitch, it was also much cheaper and easier to erect.
Have you got an awning rail on your van? I have a vango kela 3 and a vango galli for my campervan...both come with kador strip and you can get a driveaway kit, or you can get a pole and clamp attachment if there's a gutter on your roof, or you can fling some straps over the top and peg them down (this option no good if you've got a pop top though).
There are loads of othe driveaway awnings too, dependent on your budget. I thought it would be hard work reattaching...it's a bit of a faff, but not too difficult.
We had a T4 Clubman. We used to rig up a tarpaulin, but rarely.
What are you wanting an awning for? Storing kit? Extra sleeping space? Bagging your pitch? Keeping out of the sun / rain / wind? I'm asking because it might focus on a particular awning that might suit you better.