So there's a few things this conversation has sparked me to consider. Great stuff guys and I appreciate the input!
The larger RTT would be pretty much a must for me. If going with Tapui (great looking stuff, by the way) you get an "annex" that looks like a relatively nice sized "inside" area to hang out in and hide from the rain/weather/bugs whatever. However to use that the tent floor looks to need to be off the ground somewhere around 6-8ft.
Tepui Roof Top Tents - - Gran Sabana
It seems like a baaad idea to me to lift the tent that high off something like the Manley. Not to mention it would probably totally kill the ability to lift open the cover.
What about moving the RTT on top of something like this:
Cross Tread Renegade Truck Rack - 27in High Posts - 81400
That would get the height I'm after, and still let me open/fold back my bed cover to access stuff inside.
Then, if I didn't have enough room in the bed for whatever reason, suppliment with something like the non racked version of the Manley.
I know this has been done before on a Raptor but that effort didn't allow for opening the his folding bed cover and it wouldn't be high enough to use the annex either. It did look pretty damn cool though, where I think an install/setup like I'm proposing might look pretty awkward.
Also, being that high, I wonder how long 'stuff' would survive an off road trip the kind I'm used too. My TentCot literally shook itself apart, and it was just folded up in the bed.
Thoughts?