Welcome to the boards! I think whether any helper springs you get would work after a lift depends on how you lift the back. If it's just blocks in the back, the springs should still work OK. Personally, I'd put bags on it, but that's just me.
As for controllers, I can't speak to the P3, but the Prodigy is used by many on here (including me, I tow a 27 foot TT) with great results.
As for controllers, I can't speak to the P3, but the Prodigy is used by many on here (including me, I tow a 27 foot TT) with great results.