I'm not familiar with mountain maple but , if possible cut the "poles" extra long and don't seal the ends. They will check on the ends but the moisture needs a place to escape and you can cut the checked ends off. If you seal the ends and leave the bark on the moisture is sealed inside. If you seal the ends but peel the bark the moisture will leave along the pole and checking will occur. If you can split each pole in half, seal the ends but leave the bark on. The moisture will escape through the belly.
I know Gordon, OldBow, and a few other guys builds bows from similar materials and live in similar climates so they may have the solution for you.