Nitram don't be put off by the guys in here. I get the impression most of them would consider "roughing it" as having to stay in a Super 8...
Nothing wrong with going round with family members. I did a trip with my sister and GF a few years ago and have done trips with my parents and GF as well. For expensive trips it helps save a lot of money when sharing the cost and means you can spend it on other more interesting things than a hotel room. And besides, if you all want to do the same trip you may as well do it together.
Also I'd go with an SUV over a mustang any day. Depending on where you're going it'll relax you a lot as you won't have to constantly worry about hitting the car park ramps at the right angle and bottoming out the car*, and/or taking gravel tracks without worrying about getting stuck/bottoming out as well.
Definetly look into the Nationwide card mentioned above though. It'll be very useful.
Out of interest what are people's definitions of travelling light? To me that means a 40-50L duffel (or sharing a 70L) and a single 20l rucksack but it sounds like others aren't quite that "light"?
*seriously I do wonder how people get away with low cars, there are so many entrances to car parks that are reducilulouslu designed.