Jeez, I thought my 28" bunk was ok, till I read how much room everyone else has, lol - now I feel crowded. I'll probably get claustrophobic, even, having to sleep in such a tiny space! :+ Seriously, though, one way to make the bunk a good place to sleep, is to invest in the best quality bedding you can find. It makes a big difference on the nights when you're not too tired to care where you sleep.
Instead of a foldup bed, what about a blow-up bed? Placed on it's side, behind the seats, when loaded with 2 pallets, it wouldn't take a lot of room, and would offer another bit of protection from a load that didn't stay secured - just in case. I've never slept on one, but they look pretty comfy, and are available at Walmart, in the camping section.