>>your short carry to the water's edge at high tide may become a half mile walk 3 hrs later. Sandhead being a prime example...
I'd second this. Had many great holidays in the D & G area but have a good look at a chart noting low tide contours before you book somewhere. It can come as a nasty shock just how far away across sandy mud from a high tide launch you will end up at low tide.
We now tend to go a bit further northwest where most of the lochs are steep sided rock with occasional bays so there's often just a few yards from the high-low tide position.
If you don't want to go too far north and would consider a cottage Ellary Estate is small boat heaven. Choice of fair priced cottages set (mostly) around a small sheltered bay in Loch Caolisport. Estate owner keen on boating visitors and will beach launch/recover (FOC) your boat (if on a trailer) at each end of your stay.
It's a very private situation with no access from the normal public so boat security is good. You can haul a SIB just above the high water mark or with transom wheels pull it up into the garden of your cottage. There is also a small private harbour where you can keep the boat so it's ready to to go at all states of the tide.
Four of the cottages are around the grass at the top of this small sheltered bay seen in the streetview link...
Boating can be done with good safety around the head end of the loch, it feels larger scale as it broadens to the mouth and then out into The Sound of Jura for a much bigger experience.
Video of our 13ft GRP boat heading out from our last holidaycottage there...
Image of our old Zodiac in front of the cottage.
Zodiac in front of Kennels Cottage:: OS grid NR7476 :: Geograph Britain and Ireland - photograph every grid square!
Round in the next loch, Loch Sween, the same estate has caravans to let with even more boating options.