History:
10 years experience in all aspects of carpentry and building.
From 200 House sites, manor restorations and small developments.
Skills and experience have increased and grown over the years.
Answers:
Personally i would make my own lining. you'll struggle to find that off the shelf.
i'd use inch thick pse boards. thickness of stud plus 30 mm to allow for plasterboard and a couple mm for skim.
Thats something that a carpenter would be able to fit.
Would live to see some pictures of the job.... however water should not be coming in your shed end off. and you are correct, silicone is not a fix all material!
I'd recommend a carpenter/ joiner for the job.
floorbaords take a lot of wear and tear over the years. they need lifting and refixing. with glue and a mechanical fixing. that will stop any movement causing squeaking and cracking