I need to replace an air conditioner compressor unit that sits on the 2nd floor walk way on my stilt home in the Florida Keys. The walk way is 24" deep and the original AC unit fit that dimension, however, the new unit is 31" square. When I install the new unit I would like to leave a 18" space between the unit and wall to provide space to walk by. The plan is to mount a pair of aluminum channels on the deck extending out 48". The replacement AC is no greater than 175 pounds. There will be 24" of the AC unit supported by the channel and 7" supported by the reinforced concrete walk around. Question: What size channel should I use? My AC contractor is proposing 4" x 1" x 1/4" thick aluminum channel. That seems light to me. I am used to over sizing materials to afford me greater piece of mind. Also what fastener technology would be best to secure the channel to the deck.