If I remember right you live on a boat on the ocean.
So salty air and moisture.
Use oil on the guns.
A drop or two on the bolts and in the actions, and run an oily swab through the bore after you have been out shooting to slow the rust down.
About once every year or two take them apart and scrub the dust, lint and mouse nests out of the actions with an old toothbrush.
Other than that I just say regular ammo from any decent brand.