yes. That's exactly what you do!
Just remember to keep the general shape of the block smaller than the car itself.
Might take some experimenting.
Good luck
And as for your trees: everything traces back to single-celled organisms. There can't be any more trees at that point.All life that WE know.
Shame you don't have a Source version as I have a map that will never see the light of day and it's one of my best.After what happened to me in this competetion from the source engine.... I'm gonna give it a break for a little while.
You can't have monsters targeting a multisource directly. Instead, have the headcrabs trigger a button or a trigger_relay which triggers the multisource. In other words, have something in between.