We've owned 4 fivers. And the last two were pulled with a Dodge diesel dually and rightly so as their weight and size was not practical with a one ton SRW or a 3/4 ton. If your thinking of a toy hauler you're most likely, if serious about towing safely in the dually pickup territory. Most people get a diesel.
That being said we had a dually with our last two fivers and glad we did (diesel). There is nothing more to maintain in a DP motorhome engine then in a a modern pickup diesel engine. They both need the oil changed, filters , etc. The oil change if you have it done is a little more then a pickup.
The dually has six tires - our DP has six tires. If your driving the pickup every day then your going to go through tires faster than a MH most likely. The rest of the systems other then a air brake and ride system in a MH can be found on a fiver as well.
If your not driving the dually every day then your possibly paying for a truck that just sits in the drive your paying for insurance and maintenance on, no different then the MH. The exception is the MH will tow your daily drive vehicle and will make you trips more comfortable in your side trips.
There are toy hauler MH's available. We now own our year old DP MH for slightly more than our fiver and a new pickup would have cost. It can be done.