I just dropped the entire folder (Tongass Fjords X) into the P3D v5 addons folder in documents. Everything seems to work for me.
Don didn't make Tongass Fjords, That was Holger Sandman.
Don did some wonderful airports for southern BC (Victoria, Campbell River, Comox, Nanaimo, Abbotsford, & Boundary Bay) that are great places to start exploring the PNW
I think I have found the issue - there is a texture file named illum_ApronFlood.dds that seems to be the issue. I removed it and the airports loaded fine (but with no apron lights). I converted the file to 16 bit dds (it was 32 bit) and it seems to have fixed the issue.
Gavin