A friend recently gave us this Gloucester Light Dory rowing boat, which had sat for umteen years,

and which we did some basic work on to look like this:

It's 15'6" long and a faff to load onto my lad's car, much worse to get onto my van, so I went looking for a cheap trailer, up to a few hundred pounds, and found this for £425.

A trailer plus Max Craft 12' dinghy. I couldn't resist, as the lad wanted to try his Granddad's old Seagull motor on a boat and it was looking a bit precarious on the Dory. The boat is in good condition, and has the original gel coat. However, it's all a bit plastic (GRP actually) and I'd like to improve the seating. I just mocked this up with old Ikea bed boards so you can see what I'm thinking, but want something like this, so it's possible for whoever's using the outboard to move position to trim the boat.

I'd also like to have wooden slats running cross-wise on the existing seats to strengthen them (there's a small crack that weakens the central seat - we'll also reinforce this with glass fibre/ resin) and again, because it'll look nicer than grp, I think.
And so, a question. Given that the wood will be attached to the surface of the GRP seats and not held firmly to a frame, what wood is best? Having read around, it seems ply may be most suitable as it's pretty inert in sun/ water, but thought I'd ask here as some of you know best. I'd prefer mahogany, but we have to know our limits...
Also, how might we attach the wood? I was thinking maybe to make the seats as a single piece, and attach to the existing seats with resin and a few screws.
Thanks for any thoughts, Chris
ps What I've always really wanted is to build something like a Chris Craft, but time's an issue!

and which we did some basic work on to look like this:

It's 15'6" long and a faff to load onto my lad's car, much worse to get onto my van, so I went looking for a cheap trailer, up to a few hundred pounds, and found this for £425.

A trailer plus Max Craft 12' dinghy. I couldn't resist, as the lad wanted to try his Granddad's old Seagull motor on a boat and it was looking a bit precarious on the Dory. The boat is in good condition, and has the original gel coat. However, it's all a bit plastic (GRP actually) and I'd like to improve the seating. I just mocked this up with old Ikea bed boards so you can see what I'm thinking, but want something like this, so it's possible for whoever's using the outboard to move position to trim the boat.

I'd also like to have wooden slats running cross-wise on the existing seats to strengthen them (there's a small crack that weakens the central seat - we'll also reinforce this with glass fibre/ resin) and again, because it'll look nicer than grp, I think.
And so, a question. Given that the wood will be attached to the surface of the GRP seats and not held firmly to a frame, what wood is best? Having read around, it seems ply may be most suitable as it's pretty inert in sun/ water, but thought I'd ask here as some of you know best. I'd prefer mahogany, but we have to know our limits...
Thanks for any thoughts, Chris
ps What I've always really wanted is to build something like a Chris Craft, but time's an issue!