Window box liner joints
I am building a cedar window box. No issue there. I want to also build PVC liners since it is on the second floor, and it will be easier to plant in a PVC liner box and then drop it into the window box out the window. There are companies that sell PVC window box liners... they make them out of 1/8" PVC (looks like they use thicker ends, but can't see bottom in any pictures to see fi that is thicker also).
They will be about 28" long, 9" wide, 9" high. I am going to use 3/8" PVC sheet for them. A couple joinery and construction questions I would appreciate advice on...
1) Was considering using 5/8 material for bottom and ends, and the 3/8 for sides, instead of 3/8 for everything)... giving me much more area to glue/screw sides into, since it will hold a bunch of dirt. Does it sound like this will hold up to the dirt load and transport to and from window box?
2) To join the ends, sides, bottom, I was planning to glue and screw. For glues, my list of options are WeldOn 705 (like PVC pipe cement), OSI TrimTeq (seems a little better), PVC TrimWelder (seems like premium, two part product, but expense and not available locally). is the TrimWelder overkill? OSI TrimTeq good compromise? And for screws... #8, 2-1/4 white PVC trim screw... or #7, 1-5/8 stainless steel trim screw? It wont be visible. The PVC trim screws seem to have a special thread, but 2-1/4" is way more than I need... nothing else local.
I want the liners to be water tight (except where I place drain holes that will drain directly through the cedar box). The entire window box will be 10' long... with 4 drop in liners. I want to be careful of weight also. For hanging and for carrying the liner boxes.
I would appreciate advise on best way to build these.