A mucous blob is not going to roll out of a spaceship. They need dexterity and building and survival skills. And obviously extreme intelligence.
And evolution would dictate that they have a humanoid form.
That is a rather silly assertion. What makes you think that the only body form that is dexterous and can be intelligent is the one we currently occupy? That is false with even a modicum of thought. The form that a particular intelligent life is going to take if there are some out there are going to depend on the conditions of the planet it evolves on and also on the other forms of life that it is competing with.
It's taken a lot of thought actually.
Evolution works on limited resources. Almost all of our resources went to development of our brain. That's why we are weak physically. And why we don't have extra arms or legs or eight eyes. Resources were shifted to brain development. Once we were intelligent enough to invent medicine, we stopped evolving. Because survival of the fittest doesn't apply to us anymore.
All you need is two eyes, for 3d vision. Two ears for 3d hearing. Two legs for moving. And two arms with appendages with enough complex dexterity to make tools. That's a lot of resources! Not to mention our incredibly advanced brain.
Once you get to that point, evolution will stop, or at least slow down to a crawl.
Now obviously, the brain, eyes, and ears should be higher on the body to provide the most benefit.
The legs should be low to provide the most traction.
The arms should be midway to provide the most reach.
Add them all up, for an alien capable of building a spaceship, and you get a humanoid type body. Not exactly like us, but similar.