Kog'maw needs a little bit of love in terms of mana

Since the marksman rework, kog'maw's mana issues have skyrocketed, mainly due to adding a mana cost to his w. While 40 mana isn't much, with the amount he uses w, it adds up quickly. I think that kog is actually in a fairly good spot in terms of balance, I just think he needs a little help with his mana. Maybe make w cost 20 mana at all levels, or increase his total mana at level one, or reduce the cost of his e, since 80 mana hurts for something that is mainly used for zoning/kiting, not damaging. When I play him, I always seem to be out of mana, and that's without even using ult more than once.

Added: I thought of a way to change his ult while I was responding to a comment below, that might solve his mana issue as well as fit his identity better.

Living Artillery 50 mana at all ranks (maybe 70/50/30 if his early game needs the restriction). Stores charges (3 max) with a 7(?) second cooldown between shots, with 45/35/25 seconds to generate a charge.

Range unchanged, AoE size unchanged

50/100/150(+0.1AD)(+0.2AP) on impact. Leaves behind a growing AoE (similar to Cassiopeia miasma) for 5 seconds. Enemies that enter the pool take DoT(unsure of the numbers here) as long as the pool exists.