LOL, hi Sue! Yes, I was in disguise here, but as Dennis DeYoung once sang:

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On the positive side, this has given me a great idea for a world with a giant artificial trench around it... I'm not saying it was aliens, but...?

Try turning on snap to help get your marbles in row. The ortho button may also be helpful. ?

I can't edit my comment above because I haven't posted enough to the forum so sorry for the two posts, but I played with this some more and I really think that using a custom fill might be a good solution for what you want to do (minus the issue of labeling the boxes).

Here is a better example using a slightly revised version of the fill I made above (I didn't make the map itself, this is one of the example maps from a recent annual). In this example I used a polygon to draw the fill so that it only covers certain areas, which fulfills your desire to not have the grid overlap the land... you can just draw it on the water.

Revised tile I used for this grid:

I've been doing a lot of mapping lately and have really fallen into Exotica, which is a genre of music I had never heard of this time last year - think of the sort of 50's-60's jazz that you sometimes hear in really old scifi movies mixed with the background music of a downscale Tiki bar in some truly strange ways. Anything by Les Baxter, really keeps me moving while I'm working without requiring too much attention. There's a lot of it on Spotify in various playlists. ?