Third Amendment No Soldier shall, in time of peace be quartered in any house, without the consent of the Owner, nor in time of war, but in a manner to be prescribed by law.
Remember the context and the reasons the Constitution was written. It seems strange to us that a patriotic citizen would deny boarding for a member of the armed forces should they request it. This is another clear example of how the Constitution was written to limit the powers of our Government, even of our military.
British soldiers treated America's citizens like they were subjects and would demand entry into a home, food and boarding to rest before returning to battle to defeat American citizens in the war. The Founding Fathers did not want a government to grow so powerful that the citizenry be at the mercy of the governing forces.
The Third Amendment upholds private property rights of the American citizen, while it is his property, it is not to be seized, even temporarily, in peace or in time of war. A Christian should respond in mercy and compassion to someone in need, but an American need not surrender the control of his property.
When this was written, it was to protect citizens from the government coming in even as a military force and taking property that did not belong to them. The Founding Fathers wanted to prevent the government from infringing on the rights of the citizens at all costs.
So if there is a true need and one of our military needs help, I would respond in compassion and do what I could to help, even if it weren't a lot. But if it were a situation where the government through the new civilian army that this administration has started that is just as strong, just as well funded as our military or the seizure was for a political advantage in fighting against liberty. I would stand firmly on my rights under the third amendment and deny entry, board and food for anyone.