Re: Advice on Manston to Sunderland trip
I dont beleive the leg length really matters. In good flying conditions 3 hours is a relative breeze! What does matter on longer trips is of course the diversion options en route if the weather is less good than forecast and less good than you are comfortable with and of course if you just feel you need a break. Personally I always plan a couple by just making sure the airports concerned will accept me and doubtless you will have all the other information to hand.
Your first decision will be whether to route over the sea. I would personally avoid doing so, and plan the Sherness VRP, then Southend, somewhere just east of Cambridge (which provides the first good diversion, rest stop), then on past Coningsby and Waddington (you will get a transit through their MATZ without any problems), shortly after which Humberside or Sandtoft provide good diversions, and finally clearance passed Linton will also not be problematical.
The route is straightforward with plenty of good visual features if you are not using a GPS, excellent LARS cover and no high ground of concern. As suggested there are no dangers areas to avoid.
There is unlikely to be a problem routing through any of the MATZs so plan to do so.
The scenery is OK. My last trip that way was up to Dundee from the south coast, with stops at Humberside and Southend going, direct coming back. Most enjoyable.
Good luck. Let me know if I can be of further help.