Ghost sleeps with his back to Soap. Always.
Soap thinks this means that Ghost doesn't like him. Doesn't want him close, doesn't trust him to keep watch while he rests. It hurts, more than it should, every time the pair hole up in a safe house, and Soap is confronted with the fact that Ghost won't even come close to baring his belly to Soap.
In fact, as Soap comes to realize, he's the only one Ghost keeps his back to. With Price, with Gaz, Ghost may keep his back to a wall, or a bit of furniture, but at least he can stand to face them as he rests. Soap doesn't know if it's just that Ghost hasn't known him long enough, or if he's done something to make Ghost not trust him, but it's been eating away at him.
Ghost, meanwhile, is reveling in the fact that he finally has someone he feels safe enough around to show his back to. There's no fear in him- not in his heart, not in his head- that Johnny would take advantage of his vulnerability. Relaxes only when he can have Johnny guarding from behind. The best sleep of his life comes pressed back-to-chest with Johnny, regardless of how shitty a safe-house they may be stuffed in.
And eventually, Ghost starts seeking him out on base too. Drags Johnny to Price's office for a nap, tucked into a couch far too small for the pair of them. Beneath a tree on the far side of the training grounds, well hidden between the mossy roots.
Herds Johnny back to his own room, one restless night, when they'd found each other in the base kitchen.
Ghost gets Johnny settled on the bed while he goes about getting dressed down again for bed. Johnny assumes Ghost will take the side closest to the door, to keep watch as is his want.
Instead, Ghost flicks off the bedside lamp, then climbs over Johnny to settle facing the wall. He pulls Johnny's arm over him when Johnny's too slow in doing it himself, then drops into sleep faster than Johnny'd assumed was possible.
Ah, thinks Johnny as he follows Ghost into sleep, it wasn't a lack of trust, then, at all.