Material choice for simple garage frame?

[P-plats]

I have received approval to start a simple garage for the caravan and am considering the choice of material for the frame.

The construction is intended to be like this and will be built on posts:



My question now is what material I should choose for the frame (the posts) to avoid problems with rot at the bottom of the posts?

Should I go with pressure-treated wood, or should I choose regular lumber and treat it with oil or similar?

If choosing pressure-treated, do both the inner and outer studs need to be treated?

If choosing untreated wood, what is the best way to treat them?
(I don't plan to paint the garage interior, and there won't be any interior walls)

 

[GoForIt]

Will it be open and airy, as the picture suggests, so that the timber has a good chance to dry out?

I would have used pressure-treated timber for the entire solution, for long-term durability. But certainly, the interior part could be in regular dry wood.

 

[Plupp 405730]

You can use pressure-treated wood for the posts and regular lumber for the rest and paint these...

 

[fribygg]

I would have chosen regular sawn white lumber, placed sill paper between the pier and post, left it untreated or painted with distemper paint.

Choosing planed pressure-treated wood and painting with dense plastic paint instead will spoil the appearance and create unnecessary problems and costs in the future.

 

[Oldboy]

Regular dimensional lumber should work.
I would have chosen between setting the posts in raw + later boiled linseed oil, roslagsmahogny, or pure wood tar as moisture protection before assembly.
As long as the ground isn't marshy and there's 1-3 dm between the post and the ground and the panel goes just below the posts, there should be no problems.
I would also leave at least a 1 cm air gap between the post and the footing, and use straight footing irons (flat steel) so that no water can stand anywhere.
I assume the panel goes outside the posts and prevents rainwater from reaching the posts.

 

[P-plats]

Sounds like I'm on the right track if I choose treated material for the posts but regular untreated for the crossbeams between them.
The panel will then be painted with acrylic paint to match the house, garage, and shed.
Thanks for all the opinions and tips, they are valuable.