A twin pump setup would prob need a "booster charge" quite often,.. I only run 1 pump at the moment tho.
I was thinking of getting a solar trickle charger too,.. just for an extra boost,.. never needed it yet tho.
I've been told that different vans using different alternators will charge aux batteries at different rates, so perhaps thats why there are a few reports of split charge relays not performing well enough too??