Our first motor home was a 35' Safari DP and having never driven one for more than a few miles, I too was having problem keeping the coach steering straight.
With some very helpful suggestions/recommendations from the good folks here, I finally determined that it was a two fold problem. First, the dealer had put 120 psi in all tires....lowered them down to about 100 psi made a big difference until I could get it weighed and put in correct pressure. Second, it was my inexperience that I was looking at the road too close to the front of the coach. Once I learned to look further out, I wasn't over correcting at every little movement.
Try these two recommendations first before you start piling on expensive mechanical changes. Get your mh weighed and then adjust the air pressure in each tire according to the tire mfg'ers specs (found on their website) and then set back in your seat and relax and enjoy the drive.
Hope this helps
Ron