using a Sawzall with fine tooth blade I cut the slot about 3/8" x 4-5" deep..bout an inch below center.....just enough for the springs to slide.
ya don't want them slopping around beating up the bucket
then drill the 2 holes thru the wood for the roof bolts and wing nuts....labelling to keep each roof for its bucket. wing nuts make it quick when attaching roofs, keeping buckets stackable.
YOU MUST put a roof overhanging bout 10" to keep dogs out
you are asking for trouble without a roof IMO
the rear window has 1/4" rat wire for scent flow thru, and drill a hole for the wire to suspend the bait cup, keeping their attn UP at the mother lode of bait.
drill a hole thru top and bottom for the t-stake going completely thru.....over by the edge so won't interfere with jaws closing, plus you will run the t-stake thru the chain ring under the bucket to keep it all together.
once trap is slide into slots, push springs down, which raises trap bout an inch
consider using pans on trigger wires, bent up 10-20*, then they are stepping on the trigger wires
my photo DOES NOT have the roof installed.