I tow our teardrop with a 2000 Mercedes A160, which has around 100HP and a 5 speed automatic. Before I had the Mercedes I towed with an 1100cc Kia Picanto with an immense 64BHP! It towed fine, a bit slower up hills but just fine.
It is really great to hear there are still a few 128's alive and well. My second car was a 1974 1100 with about a million K's under it's belt it was an amazing little vehicle! I've had five more Fiats since and lust after a 124 Coupe.
Where I grew up in South Africa most cars have a tow bar, whether they are big or small. No-one gets panicked about trailer brakes, in fact I've only ever seen them on massive 32 foot double axle caravans.
My trailer weighs 280kg empty and makes no discernable difference to the braking ability of the car. Fuel consumption drops from the usual 14-15km/litre to around 12km/litre which is still pretty good I think.
My opinion which will most likely be ignored again

is that if you are towing at legal speeds in a sane and sensible way there is no need for millions of horsepower or brakes large enough to stop the Titanic. Be sensible, and patient, and you can tow with just about anything.