it's amazing how little of dog behavior has to do with wanting to "be the boss" Sure, some dogs are naturally more dominant, just like some people. The vast majority are pretty middle of the road and go with the flow - happy to have someone else take charge.
Either way, the first step is prevention. Don't let him get under the bed. Also, have him wear a leash in the house. If he gets under the bed, say "Spot, come" and give a tug on his leash. When he comes out, reward him.
If it IS a dominant issue, you would know it. Does he willingly get off the bed if you tell him to? Does he know obedience, follow commands willingly?
It's likely that he knows that if he goes under the bed, you are going to make him get out. He doesn't want to, so is complaining to tell you that.