I will stand up for trains. I do tent and I have a Berlingo micro camper. I have done Hadrians Wall, the Thames Path, the Eskdale Way, North Downs Way, the Arran Way, Skye trail all using PT to get about or back to the camper at night. On Hadrians Wall path I noticed on Google Earth the bus stops were shown and recall a timetable also came up.
From five o clock finishes on the Pennine Way,via Berwick, and twice on the SWCP once from Bodmin and once from Poole I managed to get back to Lincolnshire on the day.
Yes you have to be flexible and have a wait or two but it can be done, plus no long or short term parking issues.
A black mark for trains is sometimes the passenger behaviour, unruly kids, drinking of adults (one lot thrown off at York). Two Hen parties on different trips I recall with distress; I breathed a sigh of relief when one party got off at Newcastle. As I had a bottle opener I did help one lot on the way to Manchester airport; very pleased I would not be flying with them.