One advantage to synthetic oil is they it withstand higher temps than dino oil before it starts to break down. We all know that MH engines are usually running pretty hot. The water temp may be ok but the engine internals and oil will typically be a lot hotter than a car engine due to the heavy workload.
A case of Mobile 1 at Costco, with a rebate, is less than $30. So for less than $5 a quart, 7 quarts plus a filter you're looking at $40 for an oil change. A dino oil change would be around $20 I guess, haven't bought dino oil in a long time. I'll spend the extra $20 at least once a year and stick with synthetic oil.