I spent some time Googling adhesives to see what I could find. I was looking for a seriously heavy-duty and waterproof adhesive. Most of my searches pointed to various American products used on kayaks, inflatables of one sort or another and they were all quite expensive. I then started looking at various UK websites and those of UK adhesive manufacturers. I ended up on the Evo-Stik website where I discovered the somewhat inelegantly name Sticks Like Sh*t all-weather adhesive. It look as though it might be the answer. It is inexpensive, comes in a 290ml cartridge and is readily available.
Before attempting to bond the soles, I stuffed the boots with newspaper so that I could bind the sole to the upper by wrapping it with string to apply some pressure while the adhesive cured. I decided that it would probably be easier to glues the soles in two goes. I made sure that the two parts to be joined together were clean and dry (apparently Sticks Like Sh*t will bond in the wet), applied the adhesive (with a caulking gun) to the sole and instep only and then brought the two together. I wrapped the boots tightly with string and left them overnight. The next day I fixed the rest of the sole. You can always add one or two stainless steel self-tapping screws, if the recipient boots have thick sole, just to make sure. If the soles are a bit bigger than those of the boots, it is a simple job to trim-off any surplus with a sharp Stanley or craft knife.
Since then I have used the boots for a regular monthly kick-sampling session which is very hard on wading boots and the soles are still “hanging on” well. The uppers are now looking pretty second-hand and as soon as I find another pair of wading boots, probably with felt soles, I will use the rubber soles to replace them. Sticks Like Sh*t has, so far, worked far better than I could have hoped.