Original Waterlox is a marine/marine-like oil based finish. I've used it long ago for finishing an exterior door and a few other projects. There may be a water based brand these days, but I haven't researched that. Oil based Waterlox will take some time to dry, hence dust nibs may collect on the surface. This will likely be the case with any slower drying oil finish. If the cabin can be maintained relatively dust free during drying time, then Waterlox is an excellent finish.https://www.waterlox.com/project-help/g ... 6093690ce7
However, I think there are some faster drying oil finishes and Waterlox may have a representative product. You might call Waterlox and ask.
Lots of floor finishes on the market. More often, these days, I've used Varathane's water based floor finish, but more so for utility projects, not for finer woodworking. Water based products are less likely to penetrate into the wood, but rather pretty much sits on the surface. West coast folks seem to like Penofin for marine finishing, more so than other finishes.
Generally, they're all pretty good products. Hell, you could even apply straight (softened/melted) bees wax and achieve a nice finish, but reapplication/scratch repairs would need to be performed often.
If your son's project is a major endeavor and/or expensive, the lumber supplier should provide a comparative sample of their recommended finish. Have your son bring them a scrap board and test a few different finishes. Contact a flooring company and ask what they recommend for DIYers.... They might even give a few sample applications or show you results of different applications.
Good luck, hope all goes well.