You have to consider that you're dragging this machine, and it is a machine, down the highway. It moves, it expands in the heat contracts in the cold, doors get slammed, awnings get blown about. Pretty much, it's going to leak sooner or later.
Just have to stay ahead of it. After or during a heavy rain I am all over my rig with flashlight looking for the slightest hint of water intrusion. I also poke around with my scratch awl looking for soft subfloor.
And, because it's a 1986 and has traveled tens of thousands of miles, every other year or so I find somebody with a SealTech machine to double check my work. Usually, a little leak or so is found underneath where the awning rail is attached. So far, nothing else has turned up.
I love my airstream, it just needs a little TLC every now and then.
Enjoy the journey,
Old (usually dirty) Nissan Titan
Old (enhanced with "male pattern baldness") Sovereign
Young, lovely bride
Goofy dog, dismissive cat