Used to tow with my Stilo Abarth.... not much help BUT
I've towed the same caravan, Eriba Triton 430GT (GLW 1000kg) with the following cars:
Tipo 1.6ie
Punto HGT (1.8ie)
Stilo Abarth
Croma 150 (diesel)
In all cases was/am perfectly happy with performance bearing in mind each of the car's relative performances.
The Tipo 1.6ie (75BHP@600rpm - 125 N·m (92 lb·ft) @3000 rpm) is probably nearest and I think inferior in performace to your 1.4 16V Stilo (please check). It towed really well provided you didn't try to push beyond what the car would easily do. True for any car, especially when towing.
The only thing I can't compare is the wind resistance/drag factor of your caravan compared to the Eriba. This could take to edge off things but can't see it being a show stopper.
My suggestion would be (assuming you can't get any actual 1.4 towing reports, or any other contrary information) that if you really like your Stilo and are happy with everything else about it then go with the Stilo. Your worst case scenario is that you it will cost you the cost of your tow bar.
Personally I think you will be OK.
A couple of other points final point.
If you have reversing sensors then if you go for a fixed/bolt-on towball then you will find that reversing sensors will pick up the towball. I got round this by fitting a dropper plate, which as luck would have it with my caravan resulted in a totally level pull. Without the dropper plate it was a slight nose up pull.
THIS IS FOR SELESPEED Cars
Towing is a breeze bar one issue. Don't get caught in traffic jams and avoid reversing especially up hill. As you already know the Selespeed heavily slips the clutch when reversing. Put a towed load, especially up hill and it won't be long till you will smell the wear. Similary, when crawling in traffic you can't just get the car rolling and take all you feet off the pedals as in a manual. You are best sitting and waiting till the gap in front of you grows so you can then start to pull and get the clutch fully engaged, hopefully without having to slow or stop again. And yes the other dick head motorist will grunt and curse, pull into the gap you have left, etc. etc. Even with a fully manual box I still follow the "create a gap/free driving zone". Ever noticed how most private truck owner/drivers also leave gaps so they don't have to keep starting and stopping (and they have crawler gears).
Still, depsite the above caution my Stilo Abarth towed for 3 years at over 3000 miles per year including 3 trips to the Italian Dolomites with no problems.