Eric
There are a lot of things that can cause the brakes to smoke any of the below can contribute to a tight brake .
1) although technically no a brake problem and hub seal leak can cause smoking and burning
2). Bad or overheating wheel bearings can contribute to number (1).
3) as you described phenolic brake caliper pistons can absorb moisture and swell in their bores.
4) incorrect brake fluid can cause caliper seals to swell and hold caliper piston/s extended.
5) bad or incorrectly installed caliper seals.( During caliper rebuild )
6) moisture the brake fluid causing rush with in the calipers ( the lowest point in the system)
CAUTION moisture also lowers the building point of the brake fluid and can lead to brake fluid boiling and brake failure.
7) caliper slides too tight or not maintained or cleaned properly.
bad brake flex lines ( as they get old the inner lining can collapse causing the flex line to work like a check valve holding pressure on the caliper.
9) a bad master cylinder or poorly adjusted master cylinder actuator rod can cause the master cylinder piston to not return back far enough to uncover the compensator port in the master cylinder causing the brakes to drag ( worst when they are hot as the fluid expands has no where to go and applies
pressure to the caliper)
10) on an air over system the treadle valve ( brake pedal) may be sticking and not releasing the brakes fully ( the pedal itself will sometimes get seized)
With that said I assume you have air over hydraulic brakes on your coach ( correct me if I'm wrong ) it may be hydraulic over hydraulic.
The easiest way to diagnose a hydraulic problem is to loosen a bleeder screw when the problem is exhibited if loosening the bleeder screw allows the wheel to turn freely the problem is likely a flex line or master cylinder and not the caliper itself
Your front brake system will have three flex lines one at each front wheel and one at the master cylinder for the front brakes .
Most of these parts are off the shelf parts used on medium duty trucks of the era ( Ford , International , Freightliner.)
BRAKE PARTS
Front wheel bearing inner= Bower #HM212049X
Outer=.Hyatt. #3782
Outer race=. Hyatt =3720
Brake flex lines. Front= Raybestos. #BH383373. = 42"
Raybestos #BH381081. = 40 1/2 "
Raybestos #BH381082 = 39 "
Front hub seal. = stemco #383-0136
Front brake rotor. = Centric 12079023
Front brake calipers = centric #14179001. Or Bendix #55252. ( Note calipers are same right and left and front and rear)
Front caliper hardware kit= centric #11779003 ( this is the guide spring and wedge kit for the caliper mounting) does one axle or two calipers.
Front brake pads. = centric #10602360. Or Dayton D236
Front brake converter with master cylinder = Haldex # N37216c
Below is a link to the centric caliper which states the piston material is steel { I'd assume stainless steel )
https://www.showmetheparts.com/centric-parts/centric-14179001.htmlHope this helps
Eric