Alignment shop wants to start with front sway bar only??

I just replaced both front and rear sway bars with the Hellwig bars. It feels much more "planted" when driving and more stable. I had only the factory installed sway bars and these hellwig units are much bigger and stronger. I think you will feel a difference but don't know for sure as I did both instead of one at a time.

I thought you had a late model E450. Signature doesn't say but reviewing posts suggests:

Late E450
Roadmaster RSSC Stabilizer/Damper
Front Tires around 60-65 PSI for 4400 front axle weight

When a Ford Twin I Beam chassis sways, it Steers! The Rear End is the Heavy End. No wonder the Brits call it "The Big End..." That's why I think you should control sway starting back there.

Also, with the late E450 using an improved Front Sway Bar DESIGN (not size, still too small) you "might" find the end link bushings are soft rubber. You could replace those with hard bushings, polyurethane, and maybe gain a little more control.

Still, I upgraded both, and added a Blue Ox Tiger Trak rear track bar. I'm glad I did all of those, but if I was to do two of the three bars, they'd both be Sway Bars.

You'll also find your coach has a steadier stance on the campsite...

You may have read that I visited The Mountain of RV Handling Knowledge, Hendersons Line Up in Grants Pass OR, and had an audience with the Prophet of same, John Henderson. We talked mostly about alignment, but my recall is that he liked Front End Alignment With Caster and/or Safe-T-Plus Damper/Stabilizer AND a Rear Sway Bar.

From my personal experience, I'd install Hellwig sway bars Front and Rear. You have a late-model chassis, 2008 or newer, right? The OEM front bar is better executed than 1992-2007 but still undersized. The rear sway bar is the same from any E-Super Duty or E450 regardless of model year. So if you want to cut your cost a little, my take would be Rear, and use Hellwig, much less expensive than Roadmaster for the same thing. By all means, do the front too if you can.

You have Alignment. You're adding Sway Bar(s). This is all good. Have you also weighed the coach and adjusted Tire Pressures?