I haven't used it on the wood in my raised bed. It's treated so doesn't need anything else.
However I have lined the inside with the stuff that goes in ponds (not the bottom, only the sides) so the wood doesn't actually come into contact with the soil, except the bottom piece at ground level, but since it is treated it's all right.

I'd also suggest you line the sides to help protect the sides and to prevent any soil washing out.

Thank you both. I hadn't thought of lining the sides.
Did you staple it to the wood Hywel?
It's a large bed with double height sleepers, I'm not too sure I can.handle all that liner..haha!
I'll see if I can.get something lighter.
Thanks again.

One thing not often mentioned about lining sides is that it helps prevent "wicking" of moisture from the soil via the wood, and thus drying the bed more rapidly

protecting the wood is always a good idea though

Yes the liner is stapled to the wood.
I would use something durable Janey, it won't be any good if it disintegrates.

Butyl pond liner is good and tough.

Thank you everyone. I shall have a look this weekend. The wood is tanelised and the soil hasn't come yet. Thank you so much for your help.