In just addressing the fuel milage for towing, part of it will depend on the ratio of the toad weight to weight of the MH. As a very broad statement, the larger the MH, the more fuel it will use. We tow a Jeep Wrangler behind a 39' MH with a Cat C7 350HP engine. The jeep is so light compared to the MH weight, that while I'm sure it decreases my milage, it hasn't been enough for me to notice.
If your MH is smaller and or your toad is larger, then as they say, your milage may vary.
Now I do have a friend that tows a 3/4 Ton diesel crew cab with a Polaris Razor in the back of it. That probably costs him a little bit in milage......
Bill