Unless they are quarter sawn they have a decent chance of changing shape.

Look in chapter 3 at figure 3-3 (page 8 of the chapter)

it shows how wood distorts in shape as moisture content varies depending on the location in the tree the wood was cut from.

Quarter sawn wood has the tangential and radial directions aligned to the board and has less change in shape from 'nominal.'

Part of the overall change depends on how large the trunk was.

At 12 inches wide it IS going to move though.

The gaps between boards and thickness will vary significantly.

Checking (splitting that starts at a cut end) may also be more likely.

There is NO finish that will prevent the movement, just slow the water going in and out of the wood slightly.

Larger dimensions have more movement.

Here is a link that might be useful: Wood Handbook