Are there posted rules for the lava hexes on the Lost Legion maps? I figure that there's auto damage walking into them and it stops movement. Of course flight has no penalty.

The original maps (either A1 or A2) also has single (or is it double) hexed lava, so lava is nothing new as a terrain type. The ruling is no damage.

I think a additional rule "1 damage for non flying models" is very good. I will use it

Our group may try a different approach to houseruling lava hexes:

A lava hex is a hindering terrain that counts as 2 hexes when moving out of it for non-flying single based units. The movement penalty simulates ground troops crossing lava hexes slowly by way of makeshift gears. Larger units are penalized enough since they already have to make another pit stop when the 2nd part of their builk touch down on the lava hex.