OK if the weather forecast is saying torrential rain throughout the period you were hoping to go away then maybe not such a great idea. However a mixed forecast , I say go anyway. Just be prepared. Make sure you take the right kit for in tent cooking, and perhaps if the weather isn’t set to look up for a while after take a nylon tent so it will be easier to dry.
Having said that canvas tents so much nicer to be in when it’s raining, a nicer sound and with a wood burning stove still nice and cosy.
As far as what to wear, I was once told by one of the organizers of The Big Green Gathering Festival that there is no such thing is bad weather, only inappropriate clothing. The timing was absolutely perfect as we waded through thigh deep sloppy mud.