growing brassicas in poly sheeting

i have been growing my brassicas in black poly mulch sheeting  for two years now as it only lasts one season i am thinking about growing my brassicas i a much stronger black poly sheeting hopefully to last several seasons i have had good results from using poly mulch sheeting prior to using the sheeting we had problems with red-shank weed using the poly sheeting  has stopped the weeds from smothering the plants the thing is  when i lay the sheeting down i mold up the soil on the edge of poly sheet and we get re-shank growing up on the exposed ground 

so i intend to lay a complete poly sheet covering all the ground and set the plants in the poly sheeting i just wondered if anyone has tried this method do you think there's any down side to this method using thick poly sheeting rather than the poly mulch sheet as i said red-shank is very per-fuse on our lottie i have to say the wife suggested using the poly mulch in the first place it was a good idea enough said