You do not want restrictions (squishes) in the dryer vent. If the vent is already through the floor and into the crawlspace, I don't see the difficulty of elbowing toward the skirting and installing a vent kit through the skirting? All you should need to do is extend the 4" vent pipe down leve...

One of the mobile home supports is in the way. I would have to go around it. So there would be 3 elbows in the system. Is that ok to do? Also is it safe to have it go out of the dryer at 4" then squish the tube to fit through the floor at 2.5" then back to 4"?

After buying my mobile home I found that the dryer is vented to the underneath of my place. I want to have it going to the outside. But there is only 2.5" of space between the floor joist and furnace ducting. What do I do?