Pretty much, yes. But, get ready for THE messiest job you'll ever undertake on your airstream. Lot's of dirt and mouse droppings will be falling out while you remove the belly pan. Protect yourself and anyone helping you with long sleeves, goggles, and some form of breathing mask or respirator. The more you cover yourself, the better.
There's no need to add additional support under the frame just because you're removing the belly pan. If you can raise the trailer some to give you more working room, that would be good.