I did have a glance at this thread when it was active but was VERY restricted with internet and time.
We believe the most practical/cost efective way to tour Europe would be in a Euro-style motorhome around 18/20 ft---for two people.
A young couple we met in Alaska wanted to tour Europe for around 3 months--we suggested they buy a m.home, they did, and had a really good cheap trip and sold when they went back to Australia--for more than they paid---so it can be done.
It does depend on what and where you intend to visit----even a 'small' m/home can be a problem in the city centre !!!! or as we are finding in Portugal, the small villages in the mountains !! 8ft wide is great on the main roads, but narrower would be better.
when we were 'doing' city centre sight-seeing we would park in a
nearby CG and go into the city by train/bus.
If you want to go down the hire car route, try some of the companys around Lakenheath/Mildenhall (air base) they do long term hire and some will rent L/H/D cars---most don't have limited mileage.
Nigel & Pamala-------Spain