I have no idea what tent availability is in Greece, but you might look for something like this:
https://www.bigagnes.com/Products/De.../wyomingtrail2
Pricey, yes, but just given as an example of a style to look for with a tent I pulled out of the back of my head. The idea being that you can fit the bike under the extended rainfly itself, not in the sleeping portion of the tent, which as mentioned would require a massive tent. Should keep the bike out of sight, which is about 98% of it not being stolen.