I suspect they'd have wanted to shoot at Elstree for a change, just so they could have made use of the genuine sets as a costcutting measure (it worked for Carry on Cleo).
In the meantime, my fantasy casting is necessarily anachronistic, because Sid James would have to be Han Solo (in real life, he'd been dead a couple of years by the time this putative film would be released), with Barbara Windsor as Princess Leia. For some reason (mainly inspired by his role in ...up the Khyber), I can see Bernard Bresslaw as Darth Vader (probably Daft Vader in this retelling), and I kind of want Kenneth Williams as Luke, just because:
Darth: No, I am your father.
Luke: 'Ere, stop messing about!
...is an exchange I'd love to see, but really, the more naturally heroic Jim Dale is a better fit for Luke, with Kenneth better served as Tarkin.
The only problem with Bernard Bresslaw as Darth is that nobody else is really tall enough to be Chewbacca, so let's cast against height and have Kenneth Connor as Chewie. Charles Hawtrey is a natural as C3P0, and maybe Peter Butterworth as R2D2?
There really is some AU/crossover fanfic to be written here. I'm not sure I've really got what it takes to write a full Carry on/Star Wars plot, so I'll just leave this here as a plotbunny if anyone else feels like giving it a go. As for the title...I'm trying, in ...up the Khyber fashion, to work out if there can be a suitable double entendre got from ...up the Death Star trench, but it's not working. Carry on down the Exhaust Port sounds a bit weak, and Carry on Star Wars would probably have fallen foul of Lucasfilm's lawyers (mind you, this is entirely a 37 years after the fact piece of AU/crossover, so it doesn't have to be too realistic in that regard), so for the time being, I'll just leave it as Carry on Stormtrooper as per the title of this post.
Anyone else got any thoughts..?