2017 E450 based here. Somewhat larger than yours. I flat tow a Jeep Grand Cherokee. When I first got it I found it to be almost undrivable with or without the jeep on the back.
For some reason the Rv dealer thought the tire pressure should be 50 psi. Since these big class C rigs approach max weight when loaded with all your stuff the pressure on the door sticker works way better. To get it closer requires a four corner weigh. Next was alignment. Ford aligns the bare chassis so it can be driven. The RV manufacturer does NOT realign it when they are done adding all their weight and neither does the dealer.
When you get it the alignment is way off and it wanders all over the place. I took it to a well respected truck tire and alignment shop and when they were done it was like night and day. Mostly it was toed out bad from the dealer.. It is now driveable without white knuckles, even one handed. It still pushes and pulls a little when trucks pass but nothing like it was. I still might put Sumo springs on it and/or a rear track bar. The Sumo springs are supposed to calm down the side to side roll and the track bar is supposed to reduce the push and pull from passing trucks.

If I was you I would work on tire pressure and alignment before you buy any expensive parts that may or my not help.

Good luck.

Everyone will have varying opinions on these chassis I guess.

While I've never had the opportunity to drive an old M chassis, I have driven the GM P-chassis and Ford F53 chassis. Too bad, as from what I understand, the M was a well engineered chassis, and owned much of the '60s/'70s RV market.

The F53, with a solid beam front axle, has been called a LOT of things over the years. But I have NEVER heard anyone call it softly sprung or smooth riding. It's a conestoga wagon compared to a more modern independent designs. As for needing an extra leaf on one side, the chassis manufacturer has no way of know how evenly (or unevenly) the upfitter will load the thing. If your coach builder put an excess of weight on one side without compensating for it, then I'd say your issue is with them, not Ford.

GM closed all of it's medium duty operations as a cost saving measure. At the time of it's sale, it was a very popular chassis in the market place. The P chassis business was sold to Workhorse, who continued to build it (even improving it with a wider front track) for many years. That was eventually bought by Navistar IIRC, and they eventually closed it down, possibly with the demise of the GM big block. With no 8.1L power, and no gas engine of their own, there would not have been much choice. We had two in the family, with zero issues with either. If they have an Achilles heal, it's that stupid self-applying drum park brake on the back of the transmission. Workhorse pretty quickly made the move to an Allison trans behind the 8.1L, eliminating the troublesome park brake.

If getting out of the RV chassis busy in a sign the design was bad, I'm not sure where that leaves the Dodge M series, as they didn't make it past the Carter era. Or the Deere chassis for that matter.

I have an 05 F450 28' Class C with a V10 and it pulls my 24' enclosed great unless it's a windy day. Came home yesterday from the outer banks of NC and it was white knuckle all the way. Most days though not a problem at all.. It takes a while to get used to the feeling of towing the box behind you but with what you have it's a good setup. I would suggest to get rid of the Michelin tires though. That are the worst tires for any motorhome period. Every time I have used them the tread comes off like a darn recap. I have changed brand new Michelins every time I buy a motorhome with them on there. Just my opinion but be warned ..

What brand have you switched too that you like?

Part of the problem might be a Ford pulling Mopars to the track.....

What, is the world coming to?

We got a Ford towing a Mopar and a Mopar towing a Ford, I guess we have things a little mixed up. Atleast the Mopar is in a box so you can't see that it has a Ford towing it haha.

You picked your car up nicely, it looks good going down the track.

General makes a great tire that will handle the weight. I have Firestone Trans Force on my rig right now and can't say enough good things about them.

I was towing with this beast....

Thanks finally got it working good. Hey I have no room to talk I towed to the races for years with a damn Chevy.....

Towing with my motorhome was one of the best moves I ever made. I take my house with me every time I go. My wife likes the comfort and when you walk in the door you are home. . Most times I will spend the night at the track or a local camp ground because it pretty far for us to travel to get to a track now. It don't matter what your tow vehicle is powered by as long as you have Mopar stickers on your Trailer. LOL

My RV and I have a love/hate relationship. The only thing I work on more than the racecar is the motorhome...lol.

I would check out irv and I'm sure there is a facebook group specific for your motorhome. The Monaco facebook group and irv have been lifesavers for me.

Walking around the pits and seeing what folks are towing and knowing what they are rated makes me cringe.

My wife is GVWR expert after shopping RV's for about a year and she points them out to me now.

ProTip - Always add the AquaPure to the clean Water Tank and always filter the water going in with one of those campco filters.

I bet she has a fit when she see me towing with my LOL