Good idea.
My previous tow car was a 2008 Territory. I had polyair bags fitted and towed my 2000kg boat and my 2350kg van with 30psi in them.
They were a big help. I also had them fitted into my 2005 Pajero along with HD springs. Kept everything nice and level.
I recommend them. Just be sure to inflate them before you load up, don't try and use them to lift the rear afterwards, thats not what they're designed for, they're helper bags not lift bags.
Also keep minimum 5psi in when unloaded just to keep them in the springs.
Cheers,
Matt