I used a stainless plate with bumper protector & holes to mount the sockets , one each side. The holes were slotted so I didn't have to 'un-wire' the plugs to fit, I did need to grind off the small nuts & bolts that hold the sockets on though & cut / break away the old brakets.
I see no poblems with re-using the nuts & washers unless they are definatly 'single shot' like a hub nut. i've changed my hitch set up for various things & reused them. i just do the bolts up 'tight' with a 3 foot bar, never had one come loose.
i will admit if you cracked them off with a torque wrench set a 200lbs/ft & it didn't click they weren't tight enough!
Using a torque wrench to find the torque that a bolt was tightened to once its been exposed to the weather for some time is pointless as they will always take more to undo because of corrosion.But it does show if they were too loose!
Gareth