Evaporation when aging liquor in wooden barrels

It seems that it is normal for 3% to 5% to evaporate from the Barrel every month. If this is the case, one half of the liquor will have evaporated after the first year of aging. What should I do to offset this loss? Add more liquor to the Barrel each month to top it off? I plan to age raw Moonshine for at least one year in both 5L & 10L Barrels.