Removed tailgate handle to repair it and look what I found!!!!!
Rest of car is pretty much rust free,

There is a good repair post for this on one of @Alibro 's threads. Its not uncommon.

The joys of putting 2 different metals together, then adding water.
When I fixed mine I put a coat of underseal on it to stop it happening again.
Mike

The first two I did I used a dremel to get back to solid metal, then riveted alloy plates in the holes but I had a bit less corrosion then you. Last one I did the same but just cleaned back as best I could, used Krust to treat the rust and painted. I figured there is no point in worrying about the hole if it can't be seen.
The other problem you will have is repairing the handle as the bolts will either be rotten away or the plastic will be broken. Last couple of times I used strong silicone sealant to secure new spouting bolts and it worked pretty well.
Third post down
https://www.landyzone.co.uk/land-rover/freelander-project-iv-bertie.303953/page-4