Would like to have your opinion of a wooden,vs wrought iron or copper or metal trellis for clematis. I do not like the plastic trellis you can buy in garden centers. I figure a wooden one can be either stained or painted to match the backdrop(siding color) I'm wondering if the metal ones will eventually rust and mess up the vinyl siding?

I have used wooden, plastic and metal obelisks with no trouble. At least one of the wooden ones is suffering under the (I assume) moisture held in by the massive clematis it supports. I don't grow any in pots, so I can't help you there, except to say that most clems have big root systems.

The key is that Clematis need thin supports to wrap themselves around. I had DH build me trellises out of cedar lattice and they cannot climb it without help and they break off easily. My obelisks are thin metal and they climb right up. I didn't realize this and have tons of lattice and cedar fencing they can't climb without netting or wire added.

To me, these look too thick for climbers to climb by themselves. They would work to restrain integrifolias though I haven't had the greatest of luck with that either.

Here is a link that might be useful: obelisk

I've grown clematis on all manner of supports, some freestanding, some attached to the house or other structures - wooden trellises and arbors, fences, deck columns and supports, metal (oxidized iron) obelisks and trellises, rebar supports (fun to make yourself), a formal copper arbor and various "found" items (including a massive wrought iron screen formerly part of a theater decoration that I got from a salvage yard). Haven't had any difficulties with any of them as far as being able to train the vines to climb. Rather, once they get started, they pretty much take off on their own :-) And of course, any kind of sufficiently large woody shrub or tree works equally as well.

Many - but not all - clematis can be grown in a container. You need to do some homework to find those most suitable but generally smaller growing vines with smaller, mature root systems work best. Containerized plants take extra care and effort so if given a choice, I'd prefer to plant clematis in the ground, although I have grown some for several seasons in large containers.