Caliper body looks like cast alloy?

Is it possible to "cast" stainless steel? I don't know. This is cast. But looks totally different to my existing one.

You had me take another look.

Just posted a couple more photos.

By description on "casting" and label it is. If you look at the nuts they look like a different kind of SS.

Maybe a Stainless Alloy? I don't know.

Any metallurgists on here who can shed light on this?

 How much each?

 As an apprentice the company I worked for had a foundary that used to cast SS casings & parts for pumps that was back in the early 70's.

Martin Trailer parts have the SS caliper but not the SS Piston or SS shoes. What's the point in doing half the job?

Time will tell.

I believe Couplemate get the SS Pistons made to order etc.

I got these from Couplemate x 4 fully assembled and negotiated on price and return-non delivery of "standard" shoes not used - from QLD.

https://www.couplemate.com.au/hydraulic-brake-parts/al-ko-stainless-hydraulic-disc-caliper

https://www.couplemate.com.au/hydraulic-brake-parts/stainless-hydraulic-disc-pad

https://www.couplemate.com.au/hydraulic-brake-parts/hydraulic-caliper-piston-316-stainless

 I've had the same problem with my trailer. I service regularly and wash after every trip but the old smoking breaks keep popping up. I've put two shut off valves to close off the problem when needed. It's a get me out off the shit fix on the side of the road thing. The company that do my annual service are going to stainless calipers because of the amount of follow up work. I'm thinking of doing the same,  hope they fix the problem let us know how you go. 

 Having worked in the trailer service industry the easiest hydro calipers to service were the trigg A200s . You could remove piston and seals and clean or replace easy.  The alkos were just a throw away item. Servicing them could be done but they never worked the same.

The secret to hydro brakes where to use on a weekly basis even just to drive around the block to keep the pistons moving. 

 your SS alkos should work well with SS pistons. When you get them, pull them apart and pre grease them. 

O'h brakes. What a pain. Are stainless calipers worth the money?  I never see the caliper rusting. It is all the other parts that rust....piston, sliding pins, pads and bleeding screws. I recently did my brakes and replaced the pins and bleeding screws with stainless ones and I went composite pistons. I think the material is bakerlite. Seem ok. We will see how they go. So far so good. Perth Brake parts has them and similar price to standard pistons. I was not aware you could get stainless pads. Not cheap though. Perhaps next service. Would hate to know what those calipers cost judging by the pads.

I turn my brakes off when I back the boat into the water so the piston and pins don't move,  and after I hose down at the end of the day I go for a quick drive and manually activate the brakes whilst driving. Heats them up and dries them out. Find that helps prolonge the life. 

I've embarked on the stainless journey for my Ace trailer. I do one extra bit each year as I replace the brake pads (stainless) and bearings.

First I replaced all the brake lines with flexible stainless brake lines. The fittings into the brake calipers were completely corroded.

Then I fitted stainless brake calipers, the pistons etc on the old ones basically fell apart in my hands....just to respond to the question above.

Next I fitted stainless caliper holders, with stainless bolts replacing the old steel ones.

Then stainless rotors.

Now I only have one bit left.....the hubs.

It's an expensive job, but not too bad if you do one component at a time. I bought all my components from Transtyle Trailers on the east coast...I can recommend them