Blimey where to start. Yes, I've used a motorhome for the last 14 years and used it frequently over those years to walk in the Lakes. I finished the Wainwrights off this year and the motorhome was invaluable over the winter gone to assist the finish. I don't know you're knowledge of the Lakes but as you visit more and gain more hills I think you will realise your question is quite generalised
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I could give you areas you can access the hills from but in general they are on the roads and are car access points also. My last motorhome ( I've had 2) was a Trigano panel sized van which is not much wider than a car was ideal for The Lakes, having said that larger motorhomes manage just fine.
I'm struggling to think where I have struggled with access, even single roads such Seathwaite or the back of Latrigg were fine with the motorhome, passes too ( with the exception of Hardknott never tried that one with a van).
You might find the quieter months are better with a van. There is less traffic on the roads, parking is easier and if you intend wildcamping you might settle easier if you are new to it if there less traffic around.
If you have an area in mind please advise and I will if possible advise.
