Dgludwig, I went through the very same analysis several years ago when I got seriously back into canoeing, camping and deer hunting. I ended up buying the GP100 in 6".
I like round butt Smith & Wesson and Colt revolvers for carry but I thought the GP would be a better bet for a woods gun because I like to load 180 grain ammo when I camp or hunt and the GP100 is very comfortable to shoot with full power .357 magnum loads. I also like the provision for easy field stripping of the GP100. You may never need to field strip the revolver while on a camping trip, but it's nice to know that you can do it without removing small screws, springs and other little parts. You can use the rim of a cartridge to remove the grip screw of the GP and no tools are necessary other than that. If you have a screwdriver or multi-tool, fine but if you don't, it's still fine. The Ruger is designed to be more of a survivalist or military style revolver, to be serviceable in the extreme. I'm not going to remove the side plate from a S&W or Colt revolver while in the woods or in my canoe or at night by moonlight. Some others may, but I won't.
Most of my camping is done in the fall when days are short and light is short. You want your gun to be as simple as possible in that situation. The Smith is a great gun but the Ruger gets the nod when conditions are dirty, wet and nasty.
In the fall I usually spend a few days in salmon streams with waders and I took to carrying the GP100 in an Uncle Mike's shoulder holster to keep it accessible and dry. When I hunt, I carry it in a Bianchi Cyclone leather belt holster and it feels good that way. You have been shooting a long time and you already know that the right holster makes all the difference when carrying a pistol. I believe the Bianchi Cyclone is the right holster for me to use with the GP.
At the time, I agonized over whether to buy the 4" or 6" and I reasoned that the weight difference is not great since both guns are rather large and require some type of cover garment anyway. The 6" barrel gives me a more comfortable and more confident feeling when I'm in remote areas and wide open spaces. I didn't consider the 3" at the time because a deer hunting revolver is required to have at least a 4" barrel in states where I hunt.
My experience with the 6" GP100 leads me to want a 3" version for concealed carry but I honestly don't need the 3" because I find it far easier to conceal my 2" Detective Special when I'm about town. I find the 3" GP too heavy for my every day carry but it would be fine as a camping sidearm since I'm dealing with an entirely different style of clothing in a camping situation. I don't think I could effectively conceal the 3" GP in my lightweight spring and summer business clothes.
If weight matters to you more than the other things I mentioned, then the Model 65 is the way to go since it is more streamlined then the Ruger. If you spend a lot of time on your feet while camping or hiking, this weight difference of a few ounces will be magnified with each passing hour. If you are indifferent to the extra weight, then get the Ruger.
With due respect to the venerable Model 65, If I were you, I would buy the 3" GP100 because it is 6 shot, short barreled, easy to field strip and clean and good looking. It's everything you asked for and I don't see how you would regret it. Personally, I would consider going for the Wiley Clapp version although I don't know what it costs.