When I first got the Explorer (but after doing the "ziptie mod") I was averaging closer to 15 l/100km (15-16 US mpg). General maintenance helped but I think the biggest difference was slowing down a bit and removing the roof-rack cross bars.
It is a 4x4 auto with 4L V6
I went an ordered a Scangage and I will lower the front a tad before my next wheel alignment to see how much difference it makes.
I am surprised by how much you say the arena board expended for you ecomodded. I never had any problems with it but mostly use the stuff for winter applications (snowmobile skid-plates, slider protectors, toboggan bottoms, etc.
I figured it would be ideal since it is pretty sturdy, will flex on impact, is slippery and impervious to water. There might be some in one of the old barns back home. I will see if I can test some with heat and see what happens before I buy anything.
If I do the belly pan I will probably just start with the area from bumper to front axle first and see what happens. The spare is tucked up pretty well and is going to stay where it is. I would like to keep my cargo area for cargo.
I do the cardboard grill block in winter, generally it comes off as soon as it warms up enough for the cardboard to get soggy from melting snow
Another mod I forgot to ask about is wheel covers. Why is domed considered better than flat? I could make some removable flat ones pretty easily. Obviously they would come off when going through a lot of mud or snow.