I cannot remember when a state exercised is right under Article 5 of the Constitution to ask for a convention. Go Wisconsin.
For those that don't know, Article 5 provides two methods of amending the Constitution. One way having the amendment proposed by congress is the usual way. The second way is to have 2/3 of the states as for a convention to propose a specific amendment. The convention is for the specified purpose of the single amendment, not a convention to write a new constitution.

I support the idea, but how do you make exceptions for war or national emergency without those exceptions being abused as loopholes?

We should still try. I favor an appointed fiscal policy board that sets what the deficit or surplus must be. They wouldn't tell you how to get there, tax/spending hikes/cuts. They'd just tell what the deficit/surplus needs to be. They would take into account national emergencies and the benefits of paying down debt faster during the good times.

I feel some additional information is worth knowing:
a) While the Constitution allows for the state congresses to initiate the federal constitution amendment process, it has never been done. Every amendment we've ever had was initiated by the federal congress.
b) When the federal congress initiates an amendment, precise amendment language is written up and nothing happens until enough states approve (ratify) it.
c) If the states are successful in triggering a constitutional convention, that convention has full control to do whatever it pleases even to the point of completely ignoring the initial reason for the convention and discarding our present constitution. (That's how we got the one we have now). Any proposals still have to be passed by the federal congress and then ratified by enough states.
Some people feel a constitutional convention is a very dangerous thing that could be usurped to nefarious ends.