Hi...Welcome. I am not sure if the wiring is in place on a 68. It was not on my 66.
Middle vent is the place for it.
There was no existing vent line on the 66.
Check the AC you buy. Some do require a drip pan....some don't.
On my 66 I went with a 15000. I spend all my time in hot humid areas and an 11000 - 12000 would not be good enough.
Pull the vent and check for bracing in place. Easy enough to install.
Pictures are welcomed here. Check the trailer Forums...top of the page....and search for info.
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