A trip to Hobby Lobby yielded most of the items for the cushion and covers.
This fabric had the vinyl-leather look, so it was the winner. Here's a scrap for color:

Next was padding. I ended up going with 2, 76" rolls of 2". In hindsight I might have gone with 3" if I was ordering it custom, but they only had 2" rolls at the store and I had some great help on hand for the holidays.

We re-did our kitchen last year and the scraps and leftover wood product continues to be a good source of building materials for trailer and house projects. The bases for these seats used to be cabinet doors. I think they're made of 3'4 plywood circa 1980. It's solid stuff.
Lastly we utilized gray speaker box fabric to pre-cover the cushions. This provides a smooth edge to each cushion and allows the fabric to have a more finished look. I think I ordered it on amazon for $25 for a 25' roll that is 3' wide. I had a 3/4 roll left over from covering the bed on this trailer.
We started by cutting the foam with a serrated bread knife and cutting the gray fabric to wrap around the edge. We cut the fabric ~4" wider than the wood panel all around. Having fabric scissors make it easy to achieve smooth cuts. The pictured orange scissors are not them. The nice scissors only came out later when my wife realized what i was working on. She hides the good tools for fear I'll use them on something other than fabric. If I were her I'd probably hide them too.

Next, we used a staple gun to attach the gray fabric after tightening it down on the cushion.

The cushion ready for final exterior fabric:
