we found that we had to move the trampoline around. the main part was a black material and the grass underneath often got too hot and we ended up with a few dead patches over the year.
so I dont think it will be successful. But I hope I am wrong and someone can give you the advice you need.

I would have thought that Geranium nodosum wouid have been ideal for that position, given that they like dry conditions, and full shade.
You can sow the seed as soon as it's ripe, or in spring, in pots or trays, and leave outside, prick out as necessary, and grow on until large enough to plant out, Derek.

Will need watering once in position until it is established don't you think Derek?

It will indeed Mg, forgot to mention that, thanks for reminding me, lol, Derek.