Someone else put a flippac on a trailer, there's a thread
here.
But he wasn't using a longbed, looks like maybe he had it on a 6 ft bed? I'm pretty sure this one being sold will fit on a 8ft x 5ft bed when closed (that’s what mine is). Then as Troy said, you would roughly double it to get the length ... so about 16 ft? Is this the dimension you’re asking about? Yes you climb in through the tailgate, then up into the bed area.
As to the interior, nothing much there except 2 * 12V lights and the mattress in the flippy part. Everyone builds out their interior differently. I think you can make this one work if I’m getting what you’re up to. Would be difficult to photo the interior if he has it up on sawhorses. So maybe these will help:
There’s some pics of my interior and such on page 8 of
this huge thread. Mine is a full size, longbed (like this one for sale).
Louie’s amazing (very) custom build is
here. Full size, but not a longbed – regular (6 ft) bed I think.
Pics of VikingVince’s build are on
BajaTaco’s website, Tacoma, regular bed.
Safari Pacific’s super-short bed (4 ft) AT flippac, on a Ranger.
Mario’s AT flippac on a Jeep Comanche, guessing his is a regular bed? Not sure.