Shot new pics......
Design is basic cubby box. Sides slots for springs cut about 8 to 10 inches deep. Sides 3/8" plywood. Front and back is 3/4" pine board, back 3/4" longer than sides, so bottom lip extends past the sides. Trap and bait can are mounted on an inset of 1/2" osb (what I had handy) that is easy to slide in and out to load bait and set trap. Trap held in place and kept from falling out the bottom of the vertical slot by the mounting bracket and springs flexed against the side. In position, trap sits solid and will not move. Without the bracket, trap could drop out the bottom at any time. Bait placed in sardine can, which has lip all around edges, so bait will not fall out, yet animals can get to it easy.
Fixed mounting cleat is scrap of 5/4 deck lumber that box rests upon, in front is a raised cleat/lip to lock box in place to keep from falling off, insert slides down to rest upon the edge of cleat. Trap springs in the slot keep the insert from tipping forward. Whole setup is rock solid. Trapped coon drops out the bottom, box stays put.
When loaded, box is lifted into place and held in place with simple bungee. Trap is positioned halfway up the slot so when trap fires, springs can move up and down. If resting against end of the slot, top springs would have no where to go, so when trap fires, top springs would propel trap down and out the bottom. This way, it fires in place.
Simple, effective setup.