Ok, here is what happend
When you hooked the battery backwards, that is you REVERSED the POLARITY. the REVERSE POLARITY fuses in your converter blew (the two 40 amp fuses).
Dang.. To be honest that is not all that common, Normally a 40 dollar pass transistor blows in order to protect that 40 cent fuse (old Electronics Technician joke, and yes, I resemble that remark).
Well everything worked however..... Till the batteries ran down.
Now to your quesiton: will the two 30's work till you find two 40's.
Odds are.. yes. If they are working now they shoudl continue to work. In fact the "Acid Test" of those 30 amp fuses was "Did they Hold when you plugged back in after installing them) If they were going to blow.. The odds are that is when they would do it For the batteries are very very hungry.