Axle wrap is a tough one. It is a perpetual issue in the Jeep community still running leaves.
First off, any high hp vehicle running spring-over will wrap. That's just the way it is.
Some manufacturers have packs designed to minimize this. Some people have made their own anti-wrap packs. The basic idea is to add an additional full military wrap spring that has had its front cut off. This reduces wrap without increasing the rate of the pack.
Traction bars are a great solution. Again, several manufacturers make semi-custom weld on unit. The deal is you weld onto the axle housing and then again to the frame. Simple. You should be able to adapt something.
The issue with traction or more accurately anti-wrap bars is that they will limit articulation to one degree or another. The bar forces the axle to follow a path that is not the spring's natural path. Some of the aftermarket bars use a shackle on the frame end to address this. This is more likely to be an issue on a vehicle like a Jeep, where real articulation is needed, so not sure how relevant this is to the Frontier side of the house.
As for going to spring-under. That will reduce wrap, but creates its own set of problems. To keep the same ride height you will need to go to a pack with a significant arch. This will greatly reduce both articulation and ride comfort.
For what its worth...
-Z