Shed walls leaking

Good morning guys this seems to be a relatively common problem. We bought a shed off the internet (Dunster House) had it delivered and I’ve assembled it on a solid base of mot and flags. Since assembling it we have had consistent problems with driven rain penetration, being in the North West we will always have this weather. I have painted it multiple times with Cuprinol Shades but we still have damp patches on the inside walls. These appear worst where the panels are joined with damp patches on the OSB flooring. When assembling the shed I tried to seal the joints with silicone. Since experiencing the problems I’ve tried sealing around the external slats covering the joints to help the seal (pics attached).

I guess my questions are:
Is it normal for driven rain to “dampen” through the wood despite painting?
Any experience using Cuprinol Shades?
Suggestions for sealing the shed?

Many thanks for the consideration guys, appreciate any advice given.

Andy

I bought a few sheets of this in Homebase. It was as cheap as chips. I was able to fold it to get it into the car. It's been on the shed for years now, there is no sign of the wood rotting due too lack of ventilation either.

Water is beading on the painted surface so I have to assume it's not just soaking through the paint.
How long since you sealed the joins has it been? i.e., are we looking at moisture that came through before you sealed it?
I see evidence of guttering, so that's good.
Is there any chance it's coming in at the top and running down the join?

Many thanks for the response. I only sealed the joints a few days ago. We had more heavy rain last night and the stain on the floor appears larger. However, I guess this could be coincidental and it is the moisture that had gathered at the bottom of the joint seeping through. I’ll leave it for another few days and see how it goes. After that I may have to resort to some form of cladding as suggested by Stivino.

Thanks again for the suggestions guys.

Andy

where did that baton come from on the bottom edge it should not be there ??
if the floor is exposed you put felt/dpm or other behind the cladding never ever in front

Ohhh, do you think that could be the cause of the problem? I put it on as I was concerned that the rain run-off may be blowing under the wall onto the flooring.

Thanks for the comment.

it wont help
as i say get some material up the back so drips or splashes can only come forward