How do you gather Propulsion Elements please?
Can you only get the from live Thargoid ships or do they exist in the Titan clouds?
How do you stay free of caustic damage in the clouds long enough to collect rare items? Caustic sink ammo doesn't last forever.
Best choice will vary a bit on what ship you prefer. I've been using a Python with lots of Corrosive Resistant Cargo Racks, and room for other equipment too. A fast, reliable ship and patience if you're going to look for the rare stuff. Things will constantly spawn in, so keep searching around, don't give up after one trip around the Titan.
At Cocijo there is caustic, but no active Thargoids or pirates. With 4 Caustic Sinks equipped I got about 45 minutes of time in the cloud without re-supply, but the most effective way is to have a Class 5 Repair Limpet fitted and lots of limpets, as the caustic level is low enough that limpets can repair you faster than the damage, so you are more limited by limpets than by the sinks, but I would bring both for safety if you are unsure.
At the other 7 Titan sites there is no caustic effect. However there are Thargoid Interceptor and Sycthe patrols, that will fight with the AX NPC ships there. If you don't get too close and don't pick up any Bio-Storage pods they will leave you alone. There are very occasionally NPC pirates.
If you stay away from everyone to avoid trouble, then as there is no caustic effect you can stay as long as you like.
I've only been to Cocijo once, but it seemed like Propulsion Elements are more common there.
Make sure you aren't just looking close into the wreckage, a lot of stuff spawns several KM away from the body of the Titan, but if you are looking for something in particular you just have to be patient and cover as much ground as you can.