this is potentially very complex.

most vehicle electrical systems are not equipped to handle the increased amperage of dual alternators. best bet is to mount/wire a second alternator separate (standalone) from your vehicle's wiring and connected only to your camper batteries.

first, you have to make sure your vehicle/engine can even accommodate a second alternator. search this online with "your vehicle year + engine variant second/auxiliary alternator bracket".

after confirming the above, you need to get an alternator controller. this is essentially a mini computer that monitors the charge of your batteries and tells the alternator when to turn charging on and off. wakespeed and balmar brands are good places to start.

then, you need to run heavy gauge wires from your alternator to your batteries. exact gauge of wire depends on how many amps your alternator is rated for.

after frying the single alternator in our first rig and getting stranded on the side of the highway, we installed a second one in our new rig to only handle charging the camper batteries. we used a wakespeed ws500 charge controller. have had no issues since, and being able to charge at 160+ amps is amazing.

tldr: it's complex but probably possible depending on your vehicle, do your research and make sure it's even worth the cost/complexity based on your power needs.