Disco 2 Work light wiring

I'm looking to fit an led Work light to the left of the rear door of my disco 2. It will be fitted to the gutter on CB aerial bracket and switched on the dash. The wiring willing be direct from the battery.

When I fitted the same light to my previous disco 1 I ran the wiring up the A pillar and tucked it up between the bodywork and the head lining.

I'm now thinking it might be possible to route the wiring from the engine bay in a conduit under the vehicle. Somehow bringing it up the rear corner pillar. I would like to avoid drilling the bodywork.

Any thoughts on this?

Obviously keeping the wiring inside the vehicle is the best option.
I would first advise you to take a look on the roof, if you don't have a sat-nav aerial then there might be a blanking grommet there, about a foot to eighteen inches forward of the rear edge and along the centre line. If you do have the grommet then a waterproof fitting could well be the way to go. then you just have to run you cabling inside the roof space and down the inside of the "A" pillar.
I can understand not wanting to drill the bodywork, but it doesn't count if the hole was made by LR.

Quick question first, do you want a work lamp or extra reversing light?

I ask as I am almost certain there is an aux socket, or at least the wiring for it in the loom? (check wiring diagrams too to see if there is a perm 12V feed for a caravan socket?), if so, that's helpful as you could use that and relay it from that feed and fit a small rocker switch in a panel and next to no wiring runs outside the boot.

If it's extra reversing lights then look for some of these WOWLED® - 2 Pcs 18W CREE LED Flood Lamp Work Driving Light for SUV ATV Boat Truck brilliant lighting and low enough amperage to be wired in on a piggy back feed off the reversing lights with no extra wiring beyond the feed from the light cluster to the lamps.

If you really want a dash mounted switch I would say easiest to make a whole new loom up, piggy back fuse will allow you to take an ignition switched, live feed and you can easily mount a relay under the dash & keep switch wiring short, then run the wires up the door post and along the body shell to the rear door pillar and out from there.