AnchorSeal from UC Coatings is the best, and cheapest end sealer out there. It is used by timber framers as well as sawmills and lumber companies. Put it on as soon as you receive your timbers, or if you're doing the harvesting, as soon as they are cut to length. And you can put it on after the joints are cut on the ends. It's a wax that seals the ends and will help tenons slide into joints later.
Sealing the ends make the moisture evaporate threw the faces of the timber not the ends, hopefully preventing end splitting.
To help to prevent timbers from twisting they have to be stacked properly. First, a good support system with blocks level front to back and left to right. Maybe spaced only 2' apart. Then stack a row of timbers on the base. Then, place a row of stickers directly over the the supports on top of the first row of beams. Then more timbers. Once your pile is complete with stickers between each row of timbers, add another row of stickers,(all stickers could be 2"x2" or larger).
Then some more other lumber to weigh down the pile. You could even put some concrete blocks on top for more weight. If you do put the blocks on top, put enough to make the load even. Then you could put a rain cover over the pile, slope the rain cover to shed the water, but keep the sides and ends open so that air will flow threw your pile. Completely covering your pile could hold in moisture and create a condition for mold or fungus to grow.
The best solution to help prevent timbers from twisting is to cut the joinery now and put the frame together as soon as possible.
Good luck with your project.
Jim
PS. UC Coating can be reached at:
Click here for link to UC Coatings and AnchorSeal