One thing will always lead to another... have you looked at the photos in this thread just down the pages some rebuilding his roof... Neat photos of what to expect inside the roof area...
POPUP ROOF FIXWe camp alot in the Smoky Mtns at ELKMONT where the trees drip water for days after rain storms. Alot of tarps over thetrailers out there... I have a 20x30 tarp made up that has two holes cutout in it for the roof mounted air conditioner and the fanstastic fan. It just lays over the roof and ties down to the ground on the back side and comes out over the awning on the front side then ties to ground using those 15-foot ratchet 1/2-inch web straps. I use a couple of tent poles from WALMRT to align up the tarp with the awning when it goes over the bed ends.. Go's up in just a few minutes...
Wish I had a photo of my setup... Here is a quick photo I found on google on what someone has done using a tarp over the whole trailer.. Pretty close to what we do sometimes...

I already use 9X12 tarps over both bed ends all the time. This is what I call my poor man GIZMO. Really helps with the sun load on the tent bed ends and warmer in the winter. This dresses in real neat around the tent ends - use stretch ropes to tie it all off... The roof rain gutter on both tent ends makes a perfect spot to lay the tarps into and hold down with a long stretch rope. Then I just neatly tuck in the rest of the tarp and tie it off... Takes about 5-minutes if you start before you raise the roof...
This is my trailer setup showing these in use on my 2008 POPUP.... Hmm this is also at ELKMONT in the smoky mtns near Gatlinburg TN.

This should keep you guys high and dry until you figure out what you really want to do...
Just food for thought
Roy Ken