How did the EPDM go ?
but im going to give you a pointer place the back end 1ft or more away from the fence so you can work on it
do the same with the right side as you look at it
then make sure you really seal that corner up and whatever your going to fit onto it a warning though if pinlapping it its going to get heavy to move it back into its final place
you will need corner frame braces otherwise you will loose its squareness remeasure to check squareness as and when needed
when it sealed then put a seal edge x 3 on the ground or move it into place jack it up so you can seal to the concrete your choice
this will seal the whole of that corner up make sure your measurements are right for the last 2 pieces to be fitted to it as well
finish the last 2 pieces in your own time as the other 2 sides will be able to fasten to the new 2 pieces finally sealing the whole frame up
they wont if your fitting cladding on the front where the doors are
Ran out of work so took the afternoon off to get it trimmed up ready for cladding