I had the time to build a drip irrigation system for the greenhouse! Luckily, we decided to install a lead-through for water and electricity when building the foundations, thus it was as simple as it looks. Consisting of a soaker hose (like so, DE) fastened to the ground with simple tent stakes and hooked up to to a homemade inside water tap contraption made from common hardware store components.
It connects to our rainwater-collecting cistern-system and it works like a charm. Only thing I might add in the future is a timer (something like this, DE), but otherweise I’m really happy.