Hire a lightweight roller and roll your seeds in with that, I promise it will not hurt them. Your second question, how do I plant seeds, I simply prepare a bed of fine tilth as early in the Spring as you can, when the ground is dry rake over the surface, now if you want to sow them in rows then...
Plastic is non-porous and therefore paint won't adhere to it. Particularly where it will be damp. Car hubcaps are plastic and spray painted, but put the pressure washer near it and the paint comes off. Have a new tray fitted, you will have no more problems.
Firstly you must dispose of this dead rodent, in a sealed plastic bag. You provided every comfort and protection for this vermin. Cover in the garden in the form of the high grass. Obvious access to the house. Food and warmth from the storage. It probably died of thirst. There may be more...