Quality duct tape will do the job, Anto, so long as you put it onto new, clean mudguards, such as the SKS you're considering. It'll hold pretty much indefinitely, and you can remove it if & when you want to. (But it insists on clean surfaces, so if years from now you remove it from the inside of a well-used mudguard, and you later replace it, you'll have to be very careful to cut your new strip to fit into the clean portion of your 'guard. But that'll be an issue for things like silicone, sugru, etc., as well.)
I'd suggest Gorilla brand, heavy-duty black, excellent adhesive. The thing to remember about duct tape is that it likes to be warmed up a bit bef application. So, when you're ready to use it, get your roll of tape and rub it well with your hands; and apply it in a warmish room. Canoeists use duct tape to cover cracks (at least those canoeists who don't use trick Royalex boats that bend & absorb the socks from rocks), and I've used small amounts of Gorilla tape to hold my Hebie chainglider halves securely together.