Oban would be ideal for this but unfortunately (a) no slipway and (b) no engineering!
For the 50hr checks at least, wouldn't it be possible to get the engineers to come to you? E.g. could you land off Troon, moor at the marina there, and get Aircraft Engineers to send a man from Prestwick? Or are you not insured for salt water?
Does Langford Lodge have a slipway? Belfast City? Enniskillen (just re-opened)? Scotney Court in Kent, with engineers travelling down the road from Lydd? Shoreham Harbour (engineers from Shoreham)? Thorney Island (engineers from Goodwood)?
NS