I have done the Forth and Clyde a few times in yachts the locals are fine, even in Mary Hill and Clydebank just don’t hang about too long. Yes there is the shopping trolley/car issue but they are more of a worry if you have a 6’ keel under you. I would not stress too much about the walls a fender or 2 will be more than enough if you have a ‘D’ profile rubbing strike on the tubes? There is a fair bit of weed and some junk like plastic bags but this is not much of a hassle to deal with on a outboard.
Oh and we did get stuck in Clydebank once for a few hours dude to a dead body in the lock system at Mary Hill, the lock keeper did not like it when I asked “well can we go though if we promise not to hit it, or poke it with boat hooks”
The one thing to keep in mind is that it is a two day trip would suggest you spend the night by this place http://www.vintageinn.co.uk/thestableskirkintilloch/
good grub (standard pub stuff) but the only thing I don’t know if they have rooms? There might be a spot to camp but I can’t quite remember. We have always stopped off there but a yacht is a fair bit more accommodating that a RIB.
I have done the Cally canal in a RIB and it was really very nice and a top way to spend a weekend. Heading East to West there is a nice section just after Falkirk up to about 2 miles past the stables inn.
Which way are you looking to head?
PS: I don’t know what it is like for a RIB as I have not been up the Carron river in on but check what the tides are doing as I know there is not a lot of water at low tide.