First: As many others have suggested make sure the tires are properly inflated, and make sure the alignment is proper.. Then, once you have that there are 4 or 5 modifications you may wish to consider.. I will list them
Sway bars: Often a motor home will tend to "Rock" side to side..Leaning first to one side then to the other.. This causes the driver to "Compensate" tiring the driver and frankly making the problem worse.
A Sway bar... Cures to this.. I do not know if you can add 2
Trac Bars: The other thing a motor home can so is this. The house can move side to side over the axles.. Usually with a twisting motion.. The driver perceives this as the motor home drifting Highly exagrate it seems like he is going down the road like this ~~~~~~~ (Not to scale) A Trac Bar LOCKS the body squarely over the axles. Preventing this type of motion.. You can use two, Usually FIRST is the rear one, then the front if needed.
Finally a steering stabilizer.. The project of my day today was replacing my Blue-Ox Tru-Center. The original was defective and I got the replacement back last week, Today I crawled under and bolted it in, re-did the wiring harness (They have modified the harness, great improvement in my not very humble opinion. In fact I actually SUGGESTED one of the changes to them)
These devices are kind of like preachers.
The preacher tries to keep you on the straight and narrow
The stabilizer tries to keep you (And your motor home) on the straight and narrow as well. It does this by "Encouraging" the steering to be centered, There are a few different ways they work..
The Blue Ox product can put up to 275 pounds of force on the tie rid (Either pushing or pulling) but what's more.. If you need to for any reason (Changing load, High crown road, cross wind) You can RE-CENTER from the driver's seat.. Most stabilizers to re-center you need hammer and wrench and crawl under.. Not the Blue OX
Since this was a replacement all I had to do was drop two bolts in, put the nuts and washers on and tighten them down (Not exactly in that order)
Since this is a newer version with an improved wiring harness I also changed part of the harness.
The biggest problem they have had (Other than the defect that hit mine) is coil burn out, They told me they were trying to design a new coil to fix this problem. I told them how to fix it with no design change.. Guess what.. That's what they did, added a time out timer. You now get cut off after so many seconds.
Home is where I park it!