Reliable portable reversing camera

[littlespark]

I'm looking for a reversing camera for my van, basically for when i'm hooking on a trailer on my own.
I believe they only work when reversing, (taking power from the reversing light) but I would like it to work when I want it to, so I can check the trailer load while driving.
Do they work with Bluetooth to the monitor, or do I need to run a cable from dash to the back of the van?
I'm not wanting to drill holes in the van, so magnetic mount?
And portable so I can take it to a new van in a couple of years.

I know, quite a precise requirement, but maybe someone knows about these things.

 

[StephenRowley]

I've looked and struggled to find anything but If you ever find one let me know want one for the works van. Bluetooth no good as it doesn't had the bandwidth to handle video

 

[rsgaz]

I'm not wanting to drill holes in the van

To avoid drilling holes, there are this type, which replace one of the OEM number plate lamps...

Not available for all vehicles sadly. And non-transferable to another vehicle of course.

I would like it to work when I want it to

Mine is wired to a little on-off-on switch on the dash, so I can have it either when I put it in reverse, or on all the time the ignition is on.