The AirLock

A thing we know - never, ever open the door to the ship.

No matter how much blood, no matter how loudly they scream or how they plead, never open the door.
If you do not open the door they may die.
If you do not open the door the monster may get them.
If you do not open the door - you may live.
If you open the door the Alien _will_ get into the ship and murder everyone but the cat.
If anyone happens to survive they will be infected hosts who take the Alien on to the next ship and repeat the process.
In the end, it is only the Alien who lives.
Everywhere.
Everywhen.

Ask yourself - why do they want in?

What do they need?

They need air, food, water, and a warm, safe place to sleep.
Maybe they need some comms and something to do, maybe a book to read.

Put that shit in the airlock.

I am thinking a Winnebago in the driveway, or an old Air Stream if you're rich or lucky.

Make an airlock to receive the away team when they come ass-hauling back from their explorations.

Leave them in it for the quarantine phase, whatever happens to be the Alien gestation period.

After, when they have been proven clean, let them in to rejoin the crew.

And when the next ones come banging on the door, do not open it.

Ever.