if you want a natural look I would use an exterior spar varnish. For color you could do a whitewash finish.

If you look at the MSDS for Olympic Maximum Stain + Sealer, you will see it's
Stoddard Solvent : 40-70% - this is just paint thinner that will evaporate away, contributing nothing to the final finish

Linseed oil : 7-13% OK, but provides virtually no protection and no moisture exclusion

Paraffin waxes and hydrocarbon waxes 1-5% Likewise, little to no protection

With knotty pine, you always risk the resins in the knots and wood from affecting the color and result of the final finish. For example, if you're going to "whitewash" it, the knots will telegraph through in a few years.

If I wanted a clear film finish, this is what I would do:

* Light overall sanding to remove the weathering. If you don't have one, it would be worthwhile to buy or rent a decent random orbit sander.
* When this is done, rag on a bit of mineral spirits over a sample area. This will give you a preview of what the final effect will be without any stain. You should wipe the whole ceiling with a rag dampened in MS to get off the sanding dust.
* I would avoid a stain as pine is _very_ difficult to stain without blotching. If you must, use a gel stain. I also think pine looks best natural, so I wouldn't stain.
* [optional] Wipe on a coat of boiled linseed oil, wipe off all the excess. Let it cure for a week. This brings out some of the figure in the wood.
* Apply a dewaxed shellac such as Zinsser's Seal Coat. This will seal in the knot's resins and provide great depth and chatoyance to the pine. Let dry at least 30 minutes (not a problem as the first end will be done by the time you finish).
* Do a light scuff sanding with P320 or P400 sandpaper (I like 3M's 216U, AKA "Sandblaster") to knock off any raised grain. Do not use steel wool. You may use Scotch-Brite maroon or light gray pads.
* Apply two coats of deep base exterior paint per instructions in the link. LIGHT COATS.

Here is a link that might be useful: Paint on a clear finish

Thanks Bobsmyuncle! I am tending to lean towards this type of finish. My biggest concern however with a film finish is how long it will last. I actually considered using Helmsman Spar Urathane and I am concerned about flaking and peeling and long term maintenance.

Do you have any input regarding on-going maintenance for the film type finish you suggested? Would it be much better than just using the Helmsman?