painting new porch floor

We just had a screened porch added to the back of our house. It's really great, especially now that the weather is warming up a little here in N.C. I need to seal the floor, which is 3" plus wide tongue and groove pine - it is not pressure treated lumber. It is 12' x 13'. I have a few questions:
1. Should I paint it with a deck paint or use a polyurethane? Which would be more durable?
2. Should I sand it first? Are there any issues regarding how long a coat of paint will last if I don't sand it smooth? It has curled very slightly, but not so much as to make it hard to slide a chair, etc. There are slight gaps between the boards, but sanding won't help that. If I can paint without sanding I would be a happy camper. we don't mind a rustic look.
3. I think we're leaning towards an oil based deck paint, instead of a stained or clear finish. What brands of deck paint or clear finish are best for this application?
4. What can I do to the primer and paint, if anything, to make sure it seals the gaps as much as possible?
There will probably be other questions, but that will get me started.
thanks,
John
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Personally, I would never use any kind of paint on a wood floor...it WILL wear off..period..."deck" paint or no.
I would use transparent stain. Yes it will wear, but is far easier to recoat in 3 years...anything solid will start showing traffic wear in a month.
Second choice would be poly...but at least 3 coats since it's exposed to the weather.

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How about something like the Behr semi-transparent "Deck, Fence, Siding" Stain that I used for the deck and stairs? I got it at Home Depot and have been very pleased with it. There are also some Behr stains called "Silicone-enhanced, Weatherproofing, wood sealer-stain". these are semi-transparent also.
I guess I was concerned that since the porch floor is untreated lumber, it would need a different treatment. The deck, etc. is non-arsenic treated lumber (Cox natural select) and takes the stain very well.
Thanks.

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If you can, paint (or stain, or seal) the underside as well. That will help prevent moisture from entering the underside and lifting the finish on top.
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