There's always someone out there looking for a 'project' The Daihatsu Atrai (MPV) or the van version (Extol) or the alternative badged Toyota Sparky have, over the years, been candidates for conversion. I have recently purchased and awaiting MOT and DVLA registration on an Ex Guernsey C.I. Daihatsu Atrai (seven seater) and on MOT will arrange SORN. This vehicle has lots of endearing qualities. Small and manoeuvreable, fits in most multi storey Car Parks, Automatic, Alloy Wheels, Air Conditioning, Electric Windows and Mirrors and is the 4 x 4 version and tinted rear windows. Easily alter seat configuration (temporarily) to 5 seats or only 2.
I hope shortly to advertise this vehicle here but this is a bit of advanced warning. I already own and have on the road a 2 wheel drive version which I have used for a year now - reliable and ideal for the back lanes and narrow roads, particularly down here in Devon and other touristy areas.
Want more detail or talk turkey ?? - then get back to me - Date of this posting is 29th August 2023 - your winter project awaits!
Both Atrais (The Project version I had hoped to MOT ended up with structural problems and has been disposed of) - I only ever drove it on 2 journeys that ironically did involve using the M5 from Exeter to Cullompton - it however, like my daily use version is a 1290cc version so any comparison with the version you own is not comparing like with like so I really cannot express a valid opinion.
I would however say the my Atrai on a Motorway (the little we have in Devon!) is similar to driving a similarly powered Suzuki Carry Van - as it's light in weight it catches the wind and 60 mph is really the most I would want to drive at (both the Atrai and the Carry can achieve 70, even a tad faster) but I feel driving at that speed in that type of vehicle is being a bit reckless.
I wouldn't have thought the version you mention was really suited to Motorway driving irrespective of engine size and turbo or not - its the size and weight of the vehicle that I believe is the problem.