Koni FSDs are quite good (but not inexpensive) and are what I put on my (class C) motorhome. The variable frequency valving seems to work very nicely indeed, not being too stiff on little bumps or vibrations while controlling big ones decently.
When I replaced them, I ordered the new ones from shockwarehouse.com (no affiliation other than a customer) and went to my driveway to put them in. Changing them should be pretty straightforward. On the E series, the fronts are trickier because there is not much clearance above the top mount to manipulate the mounting nuts, but I suspect that's likely to be less of an issue on most class A's. If you aren't up for doing the work yourself, most any halfway competent shop should be able to handle it.
Assuming this is rocking side to side, improving the anti sway bar setup would help a lot as well.