Last Thursday we completed a 1991 mile journey through Nevada and Utah to Wyoming and back to Central California.
Before the trip I had FSD shocks installed in only the rear and I have to agree with tpi, above. Even though our Class C is only 24 feet long, I could still feel improved and very solid side-to-side sway control over what the stock Ford shocks provided. However, the main reason for the FSD shocks in the rear was to tame the pounding from highway cracks and expansion joints being transferred through by the stiff Ford OEM shocks. The high frequency mode of the FSD shocks in the rear definitely "rounded off" the jolting and were well worth if for us. The DW noticed the improved ride, too.
FWIW, we have a worse case situation ... light Class C, E450 heavy duty chassis, and 65lb./80lb. front/rear Load Range E tire pressures. Probably next year some time I'll have FSD shocks installed in the front.