I don't think there are any prepackaged turbo kits for the V10, particularly in a motorhome chassis (where the configuration of the space for and access to the engine might vary with different doghouse designs).
Gas mileage will not increase by adding a turbo; a turbo just lets you burn more gas to get more power. Cars and pickups that get, or at least claim to get, better gas mileage with turbo engines do so by replacing a larger engine with a smaller turbocharged engine. For light duty, which is often most driving in a car, the turbo is basically idle and the smaller engine gives better mileage; but when more power is desired, it is available. For a motorhome, much of the driving is not exactly light duty/low power, and in any case you wouldn't be replacing the V10 with a turbo V6 or something.