Frankly you don't add something like a leveling system, with the intent of recovering the cost, but to make the coach easier and more pleasant to use. Major adds, I have done to the Gemini, the HWH levelers, a second roof mounted matching AC/HeatPump, and inverter, running boards, Pleated track cab blinds, automatic satellite system, and more. Though these adds will certainly not hurt, I know I will not recover all costs.
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