Ah, memories! I was in the BTP (now retired) and for a while I was on an explosive / search team and we travelled the length and breath of England and Wales on these and similar duties.
I was on this team on the occasion of Her Majesty's visit to Lostwithiel for the 800th anniversary of the town charter. 1989 as I recall? We actually searched and sealed several locations for that visit. The overnight stabling point was, I presume, the one you mentioned. The site would have been chosen by a PolSa who has various non railway criteria to adhere to.
Anyway, security criteria apart, I think it was a lovely picturesque and interesting location. As indeed were the other locations we visited. I found Lostwithiel station and location enchanting. The stabling point, Long Rock depot and other points gave me a close up view of the railways in Cornwall. A night in a hotel in Lostwithiel and a night in a hotel in Penzance with a view of St Michael's Mount was like being on holiday! What had been a passing interest in Cornish railways and the county, now became a love affair!
Bob.
Western Engineman.