Your best bet is to rush your warthogs (including Sgt. Forge) to the left of your base, and take out the power nodes while hiding behind the ruins for cover. While you're doing this, build a lot, a LOT, of Scorpions and send them the opposite way to take out power nodes.
When the nodes are down, hide all your forces in the little area to the right of the Scarab, the place with all of the resource crates and the black box. When the Scarab is looking elsewhere, move them all out and attack the Scarab as much as you can before you have to hide again. Don't forget to use your MAC Cannon blast power.
Actually mission 7 is one of the easiest. It just takes time and patience. What I did is this: Build as many Scorpion tanks as you can.
Now, if you look around the left and right side of the maps, you wil see power nodes. Take all 7 of them out. Serina says it will only slow the scarab down, but after you blow up the 7nth one, it stops moving.
MAKE SURE YOU BLOW UP THE LAST NODE WHEN THE SCARAB IS FACING AWAY FROM YOUR BASE! Believe me, I made that mistake, got it down to 25% health, then it broke through the walls and blew up the base. Like I said, time consuming, but fairly easy if you know what to do.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.