Questions about standing seam vs. ribbed steel panel for solar module installation

Hello. I'm new to the forum and am planning on replacing an existing ribbed steel metal roof on an old barn in order to mount solar panels. The existing metal roofing sheets are in good condition for the most part, but nails with rubber washers were used to fasten the panels to the wood perlins. Over the years (the barn was built in 1980) most of the nails have loosened and the roof is leaking as a result.

I'm planning on installing a solar array on the barn roof but think that it would be best to replace the metal roof first. Initially I was leaning towards standing seam because of the reduced chance of leaking and the fact that the solar panel racking can simply clamp on the seams of the metal sheets without any penetrations. Unfortunately I was told by the new roofing manufacturer (Midwest Manufacturing) that their Pro-Snap standing seam metal roofing requires decking. That would add a lot of weight and expense to the project.

My other option would be to use their ribbed panel Pro-Rib roofing that does not require decking and could be mounted to the wood perlins, but I'm concerned with repeating the same leak situation that I'm currently dealing with on the existing vintage roof.

The other concern that I have is with the gauge of the metal in these products. The Pro-Snap is 28 gauge and the Pro-Rib is 29 gauge. I know very little about roofing, but that seems a bit thin.

I'm also wondering if it would be possible to replace the nails on the current metal roof with the modern screws that have the neoprene washer.

Sorry for all of the random details. Not sure if I posted in the correct section.

Thanks for reading my post.