Chat frame help

[TheSecretSquirrel]

I'm trying to edit the chat window, so that it fits inside a background frame that I've created.

Failing the above, I would like to be able to create my own chat frame within the already created frame (replacing the base chat in a way).

Is there any way I can change the default chat template to do this? (Changing chat would also include changing font .etc - not sure how todo this either).

[SDPhantom]

What trouble are you having exactly? I've used code similar to this to get a tooltip backdrop around a model frame.

local BorderFrame=CreateFrame("Frame",nil,ChatFrame1);
BorderFrame:SetPoint("TOPLEFT",-4,4);
BorderFrame:SetPoint("BOTTOMRIGHT",4,-4);
BorderFrame:SetFrameLevel(ChatFrame1:GetFrameLevel()-1);

This creates a frame under ChatFrame1 that extends 4px beyond the edges.
Note Frame:SetFrameLevel() controls the z-order frames are drawn within the same FrameStrata.
All children of a frame inherit the parent's FrameStrata. By default, the FrameLevel is the level of its parent +1.

[TheSecretSquirrel]

The trouble I'm having is that I want to move and reskin the default chat frame. Could I do that with the above code?

[SDPhantom]

It's one of many possibilities depending on how you want the end result to look. You asked for a container frame to wrap around the ChatFrame and this provides a way. It attaches to the frame, moving and resizing with it.