I'd be very wary of using structural adhesive, these areas are integral to the crumple zones. Welding isn't that difficult, definitely worth learning.


I've replaced lots of rear arches and spare wheel wells over the years. If you're on a budget buy an angle grinder and decent eye protection. It's much more versatile. I've got a nibbler but rarely use it. An air hacksaw is more useful than a nibbler, but obviously requires a compressor.


If you go the angle grinder route just remember not to wreck the glass in the car.

Regards


Pete