I want to cut access ports into the top of 2 s/s water tanks. I did
this a while ago on my alum diesel tanks and it was easy to put covers
back on the cutouts - the alum is 1/4" thick and takes a 1/4" fine
thread easily with bolts every 2 inches and a 1/8" neoprene rubber
gasket. The s/s is thinner and won't hold a bolt. I'm thinking of
using s/s pop rivets to hold a 1/4" alum collar with 1/4" fine
threaded holes in the collar around the cutouts in the s/s tanks - and
using 1/4" alum plate covers again. Or I could use s/s plates held in
with alum pop rivets and drill them out when I want to gain access
again in another 5 or 10 years. The tanks are 25 years old and have
not had access before - but we're very careful what we put in them -
so this is not a frequent event.

Any other good options?