Why? The virtue of a flip pac is that it allows you to use the bed of a truck as well as giving the extra space of the tent.
It would also have to be mounted on a cargo-type trailer with a bed, unless of course you wanted to "low crawl" through the lift gate in order to get into the thing (on a truck mounted flip pac you'd drop the tailgate and lift the liftgate and walk right in.)
Seems to me a flip-pac on a trailer would have the half the usefulness as a RTT on a trailer but at 2x the cost.
Doesn't make much sense.