Raised garden help

Hi!
Everyone here is so useful with help! Just saying thanks along with yet another question <grin>.
Closing out the sunroom addition thread, I have an idea to add something to my backyard. A large long raised garden box for along the back porch. The back porch is fully screened and has a 6 inch or so cement footer. I want to make organic (mostly) growing space in a semi-permanent way with 2-3ft high, 1 foot 'deep' and 16ft long boxes (8 feet each, at least 2, have room for 44ft worth before we hit the enclosed sunroom). These can be removed but are not truely 'movable' as they are gonna be too heavy.
Advice cheerfully accepted! I was thinking it would not be good to use the wall of the porch (about 3ft high, vinyl sided) for any of it but to start the boxes open to the ground at the bottom (and flush to the footer so I dont have to weed behind them).
This would allow for ground water to drift up a bit (still have to water them though).
So, start with a framed box of PT 2x4 then nail PT 1x6 to it for the 4 sides? Would I need a sort of riser every 2-3 feet to stabilize the box? This could be done on the exterior and nailed firmly through to the interior frame. I can use screws vice nails if needed but am not aware of any advantage in this sort of construction to them and nails seem easier.
Once frame is built and wood for the sides added, I was looking to fill with the cheaper 'garden soil' bags, mixed with perhaps some of the clay that may be left behind after digging out the footer for the sunroom. Clay as I recall if mixed well, helps retain water? If nothing else, will save me some $$ on 'garden soil' (aka 'top soil').
I'm not really sure what sort of exterior 'treatment' to do on the wood but it will be constantly damp on one side (inner). For 'looks' painting it a dark brown semi-gloss would be best match to rest of house. Seems we'd want to apply seal on planks then build, then paint the outside?
Details if needed: Back side of house, has a huge porch addition. A 13ft x 11ft section on the far corner is now a sunroom enclosure. A remaining 44ft section is a fully screened porch with a 'kneewall' about 3ft up covered with vinyl siding in almond color.
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Hi All! Didnt get answers so perhaps I was too chatty (long winded).
Would I need a sort of riser every 2-3 feet to stabilize the box? Box is in 8ft long sections, nailed to an inner frame.
I also got some advice from a co-worker. He said due to the size and that I'm putting it right up to the footer, I should call the city code office and make sure I dont need a permit. He added that in my area the bottom will rot out faster than I thought and I should raise the wood up off with some sort of cement blocks.

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