Hey !! my pleasure and hope it works just as great with your set up

all I use to hold it in place is black electrical tape that i use on all the edges, it matches the heat tape and looks nice. the top one is held the same way on the 2 side edges , the section where the screen is, is supported by the center brace !! but all this is ok since a plexi sits on top and keeps it in place nicely.
the best tape is the foil tape, this stuff really sticks well

but I didn't like seeing it (just cosmetic) duck tape works well too but same thing as the foil..
included a picture where you see one of the back heat tapes, this one i installed with the coper strips showing !!!! mistake

my others are installed with the other side showing, less visible..

since i cover the outside of the cages with a black aquarium back ground, everything looks nice.. I use this set up for my arboreal snakes so having the sides and back covered makes them feel more secure..
but the fact you have a 36L cage now, you can install a 18" long piece to heat more space, but this all depends on the species you are keeping in there.
if you just need a basking spot for arboreals, you want to keep one side with no heat for the snake thermoregulate, but if you keep a bottom dweller and need ambiant temps higher !! a full strip 36"l along the top and back will be better/ or maybe 24" in order to keep one end slightly cooler, then add a under tank heat matt/ or heat tape under the hot spot.
they sell by the foot, you then just cut the lenghts you need, best is to have = lenghts. 3x 12" or 3x18" etc etc.....
whatever you decide to go with, make sure that you control the heat tape with something, herpstat , VE or the likes of that.. heat tape gets hot 110-125 deg so it needs to be controlled top and belly.