I agree, with both the most practical approach and the most effective use of hybrids, but there is one additional use case to consider: regenerative braking on grade descents. While most highway driving is relatively flat, RVs tend to be used for trips into mountain areas, and braking for descending long grades is common. I would like to turn that energy into battery charge, whether to use later to reduce fuel use or to use while camped.The 'easiest' way to accomplish this would be a BAS hybrid system (aka "mild hybrid") which attaches an electric motor to the crankshaft via an accessory belt, just like the AC or power steering, etc... It would switch to 'generator mode' when braking to recharge the batteries and would apply power when accelerating at low speeds.
Another thing to consider is that most hybrid systems make the most difference at low speeds, when accelerating and decelerating often, and when idling (or not idling more accuartely). The typical RV spends most its time on the highway, not much can be done at those speeds.
Likely some, but maybe not. If the original vehicle has the engine running a high load and low speed, replacing it with an engine that has to run faster to produce the same power might make efficiency worse. RVs are typically not like passengers cars and passenger cars with big open trunks (called "pickup trucks") which have vastly more powerful engines than they need.I don't know how big of an efficiency difference there would be between your stock engine and whatever the minimally-sized engine could be, if both demanded the same power when travelling flat at highway speeds. But, some.
Unfortunately not. When you need power, you need power. The RV the OP is talking about has the new Ford 7.3L gas V8 which is designed to be fuel efficient in a broad powerband. No way you are going to beat that with anything homebuilt. In fact probably you would be worse off.It might be possible to improve a little bit of fuel economy by removing the engine and installing a smaller, undersized, more efficient engine, along with the EV stuff.
Basically a giant Prius.
You don't need most of the horsepower for general travelling, but for respectable acceleration and some hill climbing. So size a motor that can kind of keep you up at highway speeds, and then throw in the EV with some minimal amount of battery, enough to help accelerate and maintain some speed while climbing shorter-ish hills.
I don't know how big of an efficiency difference there would be between your stock engine and whatever the minimally-sized engine could be, if both demanded the same power when travelling flat at highway speeds. But, some.
Enough to be worth it? Absolutely not unless you're city commuting in the thing.
Headed through the foothills? It'll be okay. Headed through long uphills of mountain passes? You'll be puttering along.