To start with, you need to gather a good quantity of rose hips, since you have to remove the leaves, stems, seeds, and any damaged parts of the fruit. They should be picked fairly late in the season, right around the time of the first frosts - here, it can be anywhere between late September and early November. Look for ones that are bright red/orange, and firm but not rock-hard to the touch - when you squeeze them lightly, they should have a little bit of give to them. Don't pick ones that are blackened, browning, or underripe - depending on the year and the weather, rose hips can spoil on the vine, but ones that are ready to be picked should come off fairly easily in your hand.
Add a little water - between 1/2 and 1 cup - and simmer on the stove top until the rose hips are soft and easily workable. The easiest way to remove the seeds is to soften the rose hips and put them through a food mill - the old-style hand-crank mills have holes the perfect size for removing Sitka rose seeds.
The pureed rose hips will be more of an orange color after cooking, but the food mill should separate out the seeds from the pulp. Grind the rose hips in small, 1/4-cup batches - once the rose hips get plastered to the grates of the mill, reverse the mill to scrape up the seeds, and run it again. After a few minutes of milling and reversing, you'll be left with the seeds binding together into clumps, and the fruit flesh milled away. The fruit puree is sweet enough to work with as it is, but if you'd like to sweeten further, you can add white sugar, pectin, and/or spices, and cook it a bit longer on the stove to get all of the sugar and additives dissolves.
The best fruit leather is produced by dehydrators. Unfortunately, because of the extremely high humidity all year round in this part of Alaska, dehydrators rarely work here as well as they do elsewhere. Because of this, I've developed an oven-drying technique for fruit leather. You have to watch it to keep it from over-drying, but it produces good results. Spread the fruit puree on baking sheets lined with parchment paper, and level it with a bent icing knife (or a regular knife, or the back of a spoon in a pinch) so it has the same thickness all the way around. Bake it in the oven at 150-200 degrees Fahrenheit for 4-5 hours or until it can be handled without falling apart or sticking to the parchment paper. If it's done on top, but still sticking a bit, you can carefully peel it off and flip it over so the bottom side can be exposed to the warm air to dry faster.
The final product will be darker, and a bit wrinkled from the parchment paper's shrinkage as it absorbed water, but if you didn't overcook them, they should be easily malleable and workable. I find it easiest to store by cutting it into strips, parchment paper and all, and rolling them up to be stored in a sealed glass jar. That way, they will neither gain nor lose humidity, and can be kept for quite a long time.
Rose hips are super-high in Vitamin C, and when cooked like this, make a great winter snack. Unfortunately, I tend to eat mine really fast, and usually run out in January or February - long before I can make more. If you're more frugal, though, and make lots of them, you can store them until the next fall, when rose hips are back in season.