Suspension Upgrade

Hi everyone and thank you for all the info and tips posted in other forums, we have learnt so much from the people with the experience.

Sandy and I are planning an extensive trip in our 2000 model Pathfinder towing an offroad camper trailer.

We have been looking to beef up the suspension, we have sorted the spring, shocky, front struts combo, but some dealers are suggesting adding poly airbags as well.

Can we have some feedback in relation to how well they perform, are they "really" necessary and how prone are they to failure.

Thanks in advance.

Sandy and Graham