When writing the bass voice part for an SATB arrangement, what should be done so that the bass singers voice is not "swallowed" by the other 3 voices - being the lowest of all? (Also most choirs in my country are church based, and they tend to have fewer bass singers compared to the sopranos and altos).
Write higher. People commonly write the tenor part too low, which then forces the bass even lower, into a quieter part of their range (it doesn't help that usually most of the members of the bass section are not true basses, but rather baritones without good control of their upper range).
If you look at standard SATB arrangements of hymns, you will notice that the bass often moves in contrary motion to the melody, and often in rhythmic intervals in the middle of phrases when no one else is moving. This really makes the bass part pop in a way that does not distract from the song itself.
Also pick up and study some of Bach's chorales, and you will see what I mean, I think.
Use a well spaced writing technique. Especially between Bass and Tenor.
Remember that in a modern SATB choir, Soprano and Tenor are the brighter voices and Alto and Bass the darker.
So you have not a timbral continuum from Bass to Soprano.
This is very important when you want to write a transparent texture.
As you mentioned a church choir, you can cheat. Double the sung bass line with a quiet 16' organ stop!