My $0.02:
Pros:
* Lighter weight
* do not rust
Cons:
* By the time you put a canvas tent on top, ~100kg of water underneath, fill the toolbox with crap and the camper with chairs, tables, beds, campovens, etc - my gut feeling is that the weight is going to end up very similar between the two.
* the alloy won't rust, but it's probably got a galvanised steel drawbar. Steel axle & hubs. etc etc etc. Bit like saying a Defender won't rust because the body is alloy, where the frame is still steel.
* Harder to modify yourself / weld / etc.
* alloy (in my mind anyway) is prone to fatiguing over corrugations, etc, if not properly built and braced.
I like alloy campers, I would quite happily have a Jimboomba, as Beachman has. I am not adverse to them. BUT, at the end of the day, I wouldn't be drawn to alloy for the usual reasons (light weight), because I don't think there's a sompelling argument for it. On the same hand though, if I was looking at a camper and it was :
* the design I wanted
* the canvas layout I wanted
* the price I wanted
* the everythign else I wanted
Then the fact it was alloy or steel would count for a very small percentage of my choice. That's just me. If I were in your shoes, and this camper looked like it ticked all my boxes and was a good price to boot, I'd be there in no time.
Good luck!
Matto