check the age on your tires.
The "good" tire on that side is bad, as stated above, overloaded enough to cause permanent damage if the rig was driven any length of time with 1 flat.
You'll be buying at least 2 new tires.
Depending on the age of the tires (look at the dot date code on the sidewall) the best thing might be to put 2 new tires on the front, and the front tires on the rear, if all six match right now.
When we had our gasser, I checked all six tires with a good gauge each and every stop. (after I lost the first one, a messy experience)
When I got the DP, I also got a TPMS, which has paid for itself and then some by alerting me to a failing tire just before it actually failed.