Definitely go for a camera, ideally one mounted high up that looks down.
I’ve driven various vans with aftermarket parking sensors, they all seem to be faulty and either bleep randomly, meaning your colleague reverses your van straight into a fence, don’t work at all, or have blind spots. Lots of our work vans have big pole shaped dents in the rear steps between the sensors! Also, parking sensors don’t see things higher up, like overhanging tree limbs and telephone poles/signs close to the kerb when parking on a camber, not an issue in a car, but in a van they will try and catch you out!
My last van I fitted a ebay reversing camera, decent metal (and white) bodied camera up high and a screen where the mirror normally goes, my nice new shiny van has a built in one which is much clearer, however the posh touchscreen stereo has packed up and deemed ‘uneconomical to repair’ so currently creeping about paranoid that I’m going to reverse into something!