After I trued my wheels, V-brakes were good. But stopping downhill 174kg (trailer+cargo+me+bike) of total weight causes the brake pads to slip, no matter how much I tighten them. Will probably need a new V-brake set (if I can find them), once these wear away.
Stopping the extra weight downhill is also wearing away my rims rather quickly, so I'll need new ones in a couple of months probably... which will mean buying new wheels again, because rims for my bike by themselves are not available for 20" 1.75" tyres. There are many 20" rims on AliExpress which say they're ok for 1.75", but I don't think they are, judging by the measurements quoted.