Hi Hosko,
Our CT is a fully-powdercoated trailer. It's great - the powercoat is super hard and less likely to chip than paint. The downside is that once is does chip, it's impossible to touch up. You can't just buy a can of powdercoat and put it on - it's baked on. So you just touch it up with paint. It doesn't look as nice, but it protects just as well.
Of course, we got a fancy two-tone powdercoat, so the touchups stand out. If you get a flat powdercoat, paint touch-ups are much less noticeable.
Worth noting too is the actual construction materials used to build the trailer. So for our Tracky, they use galvanised "Zincaneal" steel RHS and sheet when building it, vs "normal" raw steel. This means that where I do get stonechips in the powdercoat, 9 times out of 10 it just chips through to the zinc gal coating, not to bare metal. Not as good as hot-dip galvanising the finished product, but heaps better than a thin coat of paint over raw steel.
Paint is the basic finish - nothing wrong with it, and easy to touch up afterwards. Hammertone is just a different type of paint, it's stippled so it's more forgiving of an uneven surface. IE, if you painted over some of my DIY jobs, they'd look terrible because you would see every single mistake. If you used hammertone, it would hide all my dodginess and look good. Because of this it's also much easier to touch up a section without having it stand out from the original paint. Hammertone is generally a bit harder, so it resists cracking/chipping better (but when it does chip, it chips bigger).
Galvanising is great, but as Dazzler says it's not without it's own issues. A lot of gal trailers up here, because they cope so well with the rain and the terrible conditions. But they cost more. These days, Trackabout do a gal chassis with a powdercoated tub - that's the best of both works in my mind.
Stainless is very expensive, plus there's concerns about how it (as a material) handles stress/corrugations/etc. Stainless can get brittle if the engineering/design isn't right. Likewise aluminium - wonderful if done right, but needs to be done right. Both those materials have questions over bush-repair-ability.
NB - The above paragraph is referring to using stainless/aluminium as a chassis/load-bearing material. If you just want to use it as panels, then it's a great option. I've got Al checkerplate all over the front and leading edges (IE, the ones likely to get blasted with stonechips) of the trailer, and love it. No rust, no needing to touch up, etc. I believe the current Trackabouts have stainless trim just for something different.
Hope that sheds some light. I'm not going to get into the canvas question, as I think the others have answered it well.
Good luck!
Matto
