To get brass barbed fittings to not leak on poly pipe you should use a hair dryer or a heat gun to heat the poly pipe up or dip the poly pipe end in some boiling hot water for a few seconds to soften it.
Then push the brass barbed fittings into the poly pipe fully and use a rubber hammer if needed and then while the poly pipe is still soft you can clamp it using 2 clamps.
You should not use a torch to heat up poly pipe when installing barbed fittings as the torch could melt the poly pipe and damage it.
However if you need to soften the poly pipe you can use a heat gun or if you use a torch only use it on low setting and just for a couple of seconds to soften the pipe.
I've seen some plumbers use a torch to heat up poly pipe to soften it a bit but you have to be careful when doing so.
If the poly pipe is new then the barbed fitting should go into the poly pipe with just a rubber hammer and then clamping it down should be sufficient.
I like to though use a heat gun to heat the poly pipe up just enough so that it softens.
If you're careful and only have a small torch then you can heat the poly pipe up inside and outside just a little bit.
When I first tried using a torch I melted the poly pipe but the second try I got it done without damaging the pipe or fittings.
The heated pipe being softened will seal better to the barbed fitting once clamped.
I would also recommend using brass or stainless steel barbed fittings with poly instead of plastic as the stainless steel and brass fittings hold up better and provide a better seal.
You should also use 2 clamps on the barbed fitting to provide a seal on all parts of the barbed fitting.