Hi Sandy, I used barlows with my newt and my refractor. The newt needs an MPCC at prime and the refractor has also a dedicated corrector or both will give me a bad field.
When I used a 2xbarlow on my newt I didn't have to use the MPCC although there was a very slight residual flaring on the edges it wasn't that bad.
With the refractor I tried with and without the corrector and it was obvious that the corrector wasn't needed at all when barlowing. Even easier.
So my advice is try with and without. You might get a good surprise.
PS:
This is my newt x2 and
this is my refractor x3.