~$350-450 for the Ranchos + ~$150 for SumoSprings
Rancho RS999926 Quick Lift Loaded Strut (Right Rear) $155-200 + tax
Rancho RS999941 Quick Lift Loaded Strut (Left Rear) $155-200 + tax
CSS-1125 | Coil SumoSprings for various applications | 1.25 inch inner wall height $140 + tax
Hellwig 7688 Rear Sway Bar $250 ish
Do you know what the tongue weight of your boat trailer is? If it's more than 500-600lb, you should try to make a WDH work.
Looks like it can be done according to the Googles. If it's right around 500-600lb (or less), you don't need the WDH. Either way, I would
highly recommend the Ranchos due mostly to the adjustable damping.
Oscillation forces will increase when you tow due to the increased weight on the axle, requiring more damping. Increased damping will help with the bounce, but it won't necessarily help with sag or bottoming out. That's where SumoSprings could help, albeit not a huge amount. Better than nothing. Yes, it will put more dynamic load on the other spring coils, but that's just the springs doing their jobs. If they ever wear down and sag excessive (not hugely likely), springs are always replaceable. Heck At $300-400 for the set, you can replace the entire kit (spring + shock) every few years and chalk it up to a cost of towing.