strong coolant smell inside the truck when the heater is on

The smell of coolant inside of vehicle is one of the classic signs of a leaking heater core.
Some cars will get the floor board carpet wet especially on the passenger side...but many newer ones will leak any accumulation out the same drip tube that drains out the condensate water in the summer when the A/C is on.
If is is a heater core you will also get a white smoke like film on your windshield if you use your defrost setting. If the core is leaking, you will eventually get low on coolant in rad....your durango will have a plastic coolant reservoir that will siphon into the radiator when it gets low. So fill up the radiator and fill the reservoir to the proper line and keep an eye on coolant use...
Many Dodges can have heater core leaks that will smell terrible and coat the inside of windows...and actually see the steam coming out of vents...but will use /lose very little coolant..
You can try some radiator stop leak.
It has stopped some heater core leaks, but it has a low percentage of success. IMHO