I will be heading down the night before anyway - so Hotel + parking might be the best option.....
Parking alone is c£65 range for 6th - 16th.
Hotels + parking can be had for as little as £60 but the ones in that range usually are much further away, non-chain and will charge for transfers to/from the airport.
I found the Best Western Moat Hotel at £108 including parking at the official Gatwick Long Staff Car Park.
I"ve done this option. Basically, you park at the hotel overnight and in the morning you drive to the Car Park, your Reg No is read automatically and you just roll in and park up.
The hotel is...adequate...but the LTCP is a treat.
Their shuttles are really frequent and are literally 3 minutes from the terminal. The Car Park is next door to the Hilton which is linked to the South Terminal.
When you return, you board the shuttle (which is usually waiting on the top level) and are dropped off by your car (The car park is sectioned and all bays have rows/bay numbers).
A doddle.
Want to do some of your own looking around...see holidayextras.co.uk (Cashback through Quidco too)
Alternatively, the HI Gatwick (Povey Cross Road) can be had [via HI site - scroll down for parking packages] for the same price and includes up to 15 days parking. Shuttles will add on another £10(ish) and take a little longer to arrive and get to/from the airport.
Hotel is nicer of course, but you get points, cashback also through Quidco and you don"t have to drive the car to the car park in the morning.
I"ve done both....for preference, I"d probably do the BW (which is opposite the HI anyway) as the like the car parking experience at the official Long Stay.
I would avoid AIRPARKS (careful, the names can get confused) as their facility is a fair distance from LGW and somewhat..erm...rustic. Hence the price differential.