Oh my lord......I took the camper for an mot to see how much work was left to do......and it only went and passed! I was concerned about the brakes, but the mot man said that's normal for a commer!
Not bad for a first trip[8D]
Miss-fire could be a number of things - was it popping and banging on the overrun, if so probably running a bit lean - maybe a little blockage in the carb or a leak on the manifold. Otherwise coil, points - all the usual stuff.
Temp sounds about normal, they do work hard on the M'way. Try ditching the air scoop that's fitted behind the grille and make youself one that scoops air from below the bumper, and the grille, - makes a world of difference when you're at high(ish) speeds.
Like this