I need to replace some. My house trim is a lot of 1 x 6 rough sawed wood. It's been regularly painted but still rots.

Are there alternatives similar in appearance that are durable?

If not, how should I prepare the wood when replacing to minimize rot? Most of this is alongside vinyl siding or brick.

Should I seal the joints with regular caulk? Looks like tyvek type material behind it. Anything special to do to it or the old holes?

One nasty spot is where the wood meets the roof line on the chimney.

If using wood, it is EXTREMELY important to seal end grain. Ive used spar urethane as a primer/sealer and that has worked well for me.

They do make textured plastic/wood boards that look like wood grain, but dont rot.

Heres an example.
https://www.homedepot.com/p/AZ...AF10006096/204791016

LP Smart Trim or Hardie Plank. A quick google will reveal all you need to know.

I would just check your local HD or Lowes. Mine has composite trim boards in stock. They are in with the trim/casing section, not the lumber.

From a proper lumber yard, get Centurion Primed Pine. Excellent product. I linked the "gold" product, the regular Centurion is finger jointed.

Also, there is Azek PVC Trimboard if you want truly no maintenance.

Does it need to look like rough sawn wood? If not there is a whole industry of PVC and PVC like products that simply will not rot or decay. These are perfect for painted trim and all I ever use in proximity to the ground. I and everybody else in my area uses the Azek that Arc referenced. Do once and done forever.