All runner are trailing From Dorman Red raspberries so need 3_4 wires so tie onto wire they want run down wire you be tiring runners all summer. Its less work cover area with mulch so maintain 4 inch thick that make weed barer and runner want be tied in with weeds.

Thanks for the reply, but I'd still like to put in a rudimentary trellis to keep the fruit off of the ground. It prevents disease/insects and makes it easier to maintain.

With 9ft. Bed you want need center post about any building supply have these materials in link and some 12 gauge wire I would put turn buckles on both ends. Remember just take slack out wire don't over tighten pull post over. The turn buckle and eye bolt is to small in link use at least 5/16" are 3/8". The cable clamps in second photo are installed wrong on wire meaning U bolt goes on short end wire. You can put treated 2x4 from post to post on top if post are not set in soil solid.

Here is a link that might be useful: Raspberry Trellis

I've used the green metal T fence posts and run the wire through the holes in the posts quite successfully. In a 9 foot bed, three posts should be sufficient. If the canes get super long, you might be fighting to keep then in that 9 foot region. I have a single black raspberry that has 5 canes on it all tied to 5 wires and i cut the canes back at 8 feet long.

Sharppa, can you install the T posts without a post pounder (i.e. with just a mallet)?

I was thinking I might just use some Y-shaped tree branches and rest the canes in the Y's. If nothing else works I'll just keep the canes nice and short, no big deal

Search the top of the page & you will find more trellis then you can read in an hour.
On the pea & bean form some ask for photo.
You could live under some of the trellis.

Here is a link that might be useful: trellis