Been toying around with rules for heroes in walkers. Basically came up with the following to modifiers:
1) Hero must start in walker, but can leave it, much the same as a squad. When hero is in walker they "share" health and damage. But the hero only adds 1/2 of their health to the walker not full. If they leave the walker then any damage the walker has taken is split evenly between walker and hero as the owning player wishes (meaning if it has taken 4 damage, each will have 2 damage when splitting, if it has 3 damage the player may assign the damage as he pleases, as long as one takes 1 point and the other 2 points). Abandoned walkers no longer move or fire, but still provide cover and block line of sight.
2) A hero is considered to have the special skill of PILOT when in a walker. This allows them to reroll a single die (one die, no matter how many were rolled) per round while in the walker.
Still trying to figure out who can pilot what. Thinking a walker that a hero decides to pilot must have equal damage capacity or mabe be of at least twice coressponding armor class. So a Infantry 2 could pilot a Walker 4, but not walker 3. A Infantry 3 would have to pilot at least Walker 6 and so forth.
Also working on an idea for "popping the hatch" which allows the pilot to fire their own weapons but it costs an additional action (one for the walkers a second for their own) and while popped the vehicle has its armor class reduced by 1. While popping the hatch they cannot use their PILOT skill.