I picked up some of this route the other day, joining it at Dumfries, having ridden over from Lockerbie. I wasn't on a DIY - just touring along with panniers and general survival kit. There are rolling resurfacing (spray and chip) works once you leave the main road West of Dumfries, but I expect the surface will be well settled by the time of the event. Other than that this section to Castle Douglas is fine. On the next bit past Loch Ken it is generally good going, though there are a few sections of that really rough surface they seem to favour North of the border. After Ayr, there were a number of riders using the cycle path, so I followed that for a bit and it was very good. Knowing how cycle paths have let me down in the past, I lost my bottle just before Troon and headed back to the roads. Might be worth looking at how that path continues as an alternative. Either way, this is a very 'fiddly' area to cycle through, unless you know the area well and careful prior focus on it would be worthwhile. I also went off piste at Kilwinning and ended up going through town, but was rewarded by finding a good chippy there, which was worth the extra k. By that time it was getting well into the evening and the bypass was quiet, so I stuck with that past Ardrossan and batted on up the main coast road with no problem, but I suspect a control will prevent that route! The ferry to Dunoon seems to run very long hours, so the logistics of that should not be too bad. The only problem is the pronunciation of Gourock... it does not seem to have any significant vowel sounds when spoken by some of the locals, though others seem to rhyme it with Thurrock, which should be a useful tip for any TOWIE riders. After that I cut a big corner for my own journey, up past Lock Eck and only briefly rejoined this route as I headed off for Inveraray and a bit of a kip. Nothing to do with this event, but I wouldn't recommend riding on to Oban this way in the daytime (though it was fine for me as I set off from Inverary just as the first glimmers of 'pre-dawn' were starting to show). It'll be a big adventure when this event runs and not one to rock up to without some proper planning and consideration!