Is this enough to block the Crimson?

[Infirain]

The tunnel is 5 blocks tall
I can give a video where you can see it in detail if you want to help and it will be easier for you to use that

 

[Russ Guss Doodles]

If it’s three blocks wide all the way around then yes. Just make sure you cover/replace the grass blocks at the top and make a short tower so that Crimson Thorns don’t grow across.

Something like this (the decorations and background walls obviously aren’t necessary).

 

[Infirain]

If it’s three blocks wide all the way around then yes. Just make sure you cover/replace the grass blocks at the top and make a short tower so that Crimson Thorns don’t grow across.
View attachment 432385
Something like this (the decorations and background walls obviously aren’t necessary).

Yes but I don't have any dirt blocks there and I didn't cover them. To replace the missing blocks I dug it 5 tiles wide

 

[daedaLus stormNo]

You need a non corruptable block in between there to stop vines. I reccomend rope its cheap

 

[Stellar Mastodon 267]

You can also use clay or mud. Ore just plain wood works.

 

[a really far away planet]

You need a non corruptable block in between there to stop vines. I reccomend rope its cheap

rope also can be quickly placed down which is useful