yes it can be used as a tub surround please see the link below: https://images.homedepot-static.com/catalog/pdfImages/27/27aa17c6-6e9e-46c0-bce3-98f956a745d9.pdf
I would not recommend for bathroom ceiling not sure how it would stand up to the moisture.
They make a vinyl siding product for that purpose.
You can, but there are much more affordable and efficient options. The look of bead and batten panels is available in a vinyl siding soffit panel that is 12" wide and 10-12' long. These panels would probably hold up much better for under a deck. There are also trim channels that are much more decorative than the standard "J channel". But be sure to allow a way for rain water to escape, when installing.
I would suggest gluing, not nailing. If you must nail, nail the tongue so that the nail doesn't show when you put the next board on, and only face nail where you have a trim piece to cover it. For trim, use a "pin nailer", and if you must fill any holes, use a white silicone to maintain the water resistant surface and not have any rust show later from the nails.
They make a soffit panel specifically for your project, that looks just like bead and batten, and I'm guessing would cost much less.
This comes as a box with 8 pieces in it. We cannot break open the box and ship only 1 or 2 pieces. Thank you.
Veranda HP Beadboard Panels are an exterior trim product and are not intended for use as a cladding material.When installed as a wainscoting Veranda HP Beadboard Panels must be applied over a solid substrate. Uses include: Porch Ceilings Soffit, Wainscoting Flower Boxes, Hot Tub Surrounds
This is PERFECT for what you want to use it for. It is a very smooth finish with no texture, so not sure about "wanting it to look like wood. What makes this great for a bath is that the product IS NOT wood, but plastic, so no water will ever hurt it. I would also suggest finishing it off at the base and chair rail with a plastic product as well. You may also want to use a white silicone caulk to tie it to a bath surround or other mold. I even used a plastic product for my door casing. But be sure NOT to use silicone in an area where you are going to cut in with paint, since pure silicone cannot be painted over.
This specific item is only available online as a box with 8 pieces in it. Your local Home Depot probably has something similar that can be purchased in 1 piece increments.