I am sure that for external 'A' frames soft solder would be strong enough. I agree that silver solder is stronger but you only really need it where higher temperatures are a concern and solf solder may fail, such as in steam installations, boilers etc.
If you are goping to silver solder then I would strongly recommend coated rods, no messing about with something else to think about and they are so easy and convenient.
The most important thing with any soldering is that the job must melt the rod not the flame. If you melt the rod with the flame it will never float on the job it will simply form a blob and sit on the surface. Clean the joint with wet and dry, clamp the joint carefully, paying particular attention to where the heat is going to flow away through the clamps. Fire bricks are a must to keep the heat in the job and you will need something of the size of the hand held gas bottle powered jobs available from hardware stores for a heat source.
Once the job is hot touch the flux to it and it will clean the area and flow into the joint then, when the job is hot enough, round about just turning cherry red, touch the end of the rod to the job and the rod should melt and flow into it all in one go.
If you have never done this before practise as many times as you need before you are comfortable with it. If you pay attentiion to these basics it is actually very easy but miss out one of them and it just won't happen.