Easy way to cut costs

Ever since trip computers have been around I've had this obsession to get my average MPG as high as possible. I've always thought cruise control was the ultimate feathering of the throttle valve, but it wasn't so on my Hyundai Santa Fe, however, on our current Mazda CX5 it really does bring the MPG up. When towing on motorways I stay in 5th gear and set the cc to 60mph. Easy-peasie (As long as traffic's not too heavy).

point well made and noted, although my next trip (Gloucester to Troutbeck) I need to get there before bedtime!

There seems to be a race to the bottom developing here. This has downsides. 

Firstly, the difference in consumption between 60mph and 50mph is relatively minor. The curve measuring average MPG at different speeds tends to be fairly flat between 30 mph and 60 mph. It rises steeply to up 30 and falls not quite as steeply after around 60 mph. This can vary with the vehicle of course, but that is a rule of thumb. Indeed I recall seeing various claims in YouTube suggesting that 60mph is better than 50mph, or 56mph (the level that most stats tend to be based on [I think]), in higher powered vehicles.

Secondly, and this is the more important factor for me, driving at 50mph on motorways can feel positively dangerous sometimes. It can feel very intimidating when lorries come up behind you extremely close waiting for a chance to overtake. Lorry after lorry will be overtaking and should you come against a very slow moving vehicle, for some reason (although at 50mph that won't happen often), you will cause one heck of a tail back when you try to overtake, if on a busy motorway. To be safe, you'll probably need to speed up whilst overtaking. 

I do accept, however, that towing a caravan could change things on both of these points. Having never towed I couldn't really say for sure, but I do know that it is very rare to see caravans travelling at 50 or less. I have even had caravans overtake me; I tend to cruise at 60, but sometimes less if I find myself early.           

I use cruise control on motorway sections and it definitely helps MPG.

I too was told to drive as if there was an egg between my foot and the accelerator.

Another tip, (from a chauffeur) was to drive as if you had a glass of water balanced on the bonnet! Makes for smooth driving at all times!

Adaptive cruise control really comes into its own on long sections of motorway roadworks. Knowing that it will keep the car a set distance behind the car in front is really relaxing when vehicles are bunched together. I accept that, in an emergency stop you cannot rely on it but for normal variations in speeds it is brilliant.

Keep caravan or motor home  at home and have a stay cation on drive 

I had cruise control on my old Santa Fe which I could always beat with a light right foot, however, my Mazda CX5 is very frugal on CC and I engage it as soon as I have a good clear road. The problem these days is finding a good clear road!

BTW I find no problem with the OP, especially when it comes to saving fuel, good for our wallets and the planet. 

One last point, light on the right foot also helps keep a safe distance behind the car in front, which as well as good safe driving reduces the fuel needed to return to "cruising" speed.

As a professional driver, I can add that a great deal of training goes on within the industry to achieve fuel efficient driving. It is claimed within the haulage industry that careful and considered driving can save up to 17% on fuel as well as reducing wear and tear on the vehicle. In fact, most trucks now have an uploadable data/telemetry system that monitors the driver's performance and sends it to the office for scrutiny. Some very simple tricks can also work for the car driver. Anticipation is key, look much further down the road and anticipate halts, traffic lights etc. Start to come off of the gas early and allow the vehicles momentum to do the work for you, stay off of the brakes! Accelerate gently, change gear at the appropriate revs instead of over-revving in each gear, a fault of many drivers. Come off of the gas on downhill runs, let gravity do the job for you, it is free! Cruise at the same speed as the HGVs, 56 mph, it is surprising what a difference 4mph can do to consumption. Instead of tear arsing to overtake trucks, just chill and tuck in. Get close enough behind and the truck will slip stream for you. (two second rule applies!)